Strange noise, only under load...

[Jonathan]

Ideas welcome...

Within the last couple of weeks I have heard a strange noise coming from over my shoulder when driving the car. It seems like it is coming from somewhere in and around the engine bay.

It has gotten more pronounced in the last few drives and has me wondering/worried more about what is going on.

Here's what I can tell you:

The noise is somewhat of a vibration or rattle. A flutter perhaps. You ever hum or buzz with your lips and if you do it just so, you get a tickle? That's what sense I get with this noise. Maybe metallic, maybe air.
It comes and goes only while pressing the gas pedal. And repeatable too. It won't make the noise when idling, only when pressing the gas. More so when pressing initially on the gas, or letting it off, but not so much as you settle in on a constant gas pedal pressure.
I cannot get it to repeat when parked in the garage, only when the car is in motion.

Makes me think it is RPM/load based and perhaps also related to the wheels in motion.

I thought perhaps it was a piece of my muffler heatshield rubbing against the muffler peg as you put the engine under more load. This is kind of what the sound made me think of first, but I looked over the heatshield and I'm not sure this is it. The end I thought could be rubbing, I put a small piece of foam tape just to test and the noise continued.

Next thought was a fuel injector seal leaking as I thought perhaps the noise was air rushing by in some manner. A fellow owner mentioned that since it happens only under load and not at idle, that's the opposite time to when you might hear an injector seal leaking, i.e. more likely at idle and not under load when the vacuum is stronger. I don't smell much fuel in the engine bay either. Not strong anyway, faint every so often perhaps but not super noticeable.

I stopped by a shop to talk to the guy about some work on my Pontiac and asked him his thoughts on the noise. He asked me whether it does the noise when stationary versus moving as I hadn't tried that yet. I did the test and I could not get the noise to repeat when sitting in one spot, only while moving. He mentioned how if the rear differential was quite low on oil, it might be subjecting the "roller bearings" to wear and that noise could be them wearing out. I'm not familiar with the internals of the rear differential, but since the noise only happens when moving, I agree it's likely related to the wheels in motion and not an idle engine. That might rule out the A/C belt or idler pulleys going bad. It might also be the alternator giving up if the bearings in it are going bad, but again, since it will not do the noise parked, I am thinking the rear diff idea might be the source.

Does any of that sound familiar to any of you? Any other ideas of what this could be or where it might be coming from? Any ideas for tests to do?

I can pull the A/C belt off pretty easily to rule that out if needed. I could even remove the muffler heatshield and all the brackets temporarily to see if it matters.

I can also see about opening up the fill port on the rear diff and checking the level. I have not checked this recently, not since refilling perhaps 3 seasons ago. Likely from the poor access to the fill port. Poor excuse, yes, but that's the truth. My car has been dripping some oil for a while, but have not been able to determine exactly where it is coming from. It is reddish but not pink like ATF. My ATF cooler hoses don't appear to leak and neither does my auto trans pan or dipstick. The drips that come appear right under the frame cross member which others have labelled as a main seal leak on the engine. Engine oil level has been fine each time I check it via the dipstick. Same for the ATF level via dipstick. Car is shifting fine and the performance has been good all season. If this noise wasn't there, you wouldn't suspect a single thing is wrong with the car at all.

Thanks in advance for any insight.

[opethmike]

Is it loud enough that you could possibly record in the car while driving?

[Jonathan]

Is it loud enough that you could possibly record in the car while driving?

I can try doing that. I have a couple other places to check on spots things might be rubbing against each other as well. It's almost like when you stand on the gas a little and the engine "flexes" under that big PRV power, something just comes into contact with another nearby surface and rubs/rattles and then stops once you ease off the gas. Not sure that's what is going on, but it's along those lines.

[Bitsyncmaster]

I had a buzzing sound come and go a few years ago and it sounded like it was coming from the drivers side door (left shoulder). Never could pin point it with any conditions. I've not heard it since. I actually forgot about it so not sure if anything I've fixed took care of it. I really think it was some wind noise in the top of the door.

Come to think of it, I did remove my top door seal because it would always fold over and push the T panel up when the door was closed.

[Jonathan]

I have found one fastener not in place on my muffler heatshield.

If you look at the right hand side lower bracket... http://store.delorean.com/p-6469-bracket-muffler-rh-recond.aspx

See the rectangular extension sticking out sort of on its own? It corresponds to a hole in the heatshield that's sort of in the middle... and not exactly accessible to get a bolt through to thread into the nut that's welded onto the bracket... because there's a muffler in the way!! Who thinks this stuff up??

Anyway, that slim rectangular section of bracket is all that is keeping the right side of the heatshield secured to the bracket, otherwise this "flap" could be the culprit for my vibrating noise. Maybe. Who knows. I put some double sided 3M tape on it to go for a test drive to see if that changes anything. Although getting a bolt back into place on the heatshield wouldn't be a bad idea either.

[Jonathan]

Ok, so it isn't that extension of heatshield not well secured to the bracket. At least the attempt to stick the two together and stop them from vibrating didn't change the noise.

I did not yet get a chance to record it, but it's still there. Since it is so correlated to the accelerator being pressed, I am thinking it's possible it's related to one of the moving pieces in the fuel system. Like the idle speed motor rotating or the fuel distributor stem going up and down. Maybe one of those is sticking or whining or something and making this whistle noise business. I kept it in mostly the neighborhood on this last test drive and the noise is more pronounced when you are easing/coasting towards a stop sign and then give it some gas just to get you up to the line. Like if it is idling and then you give it a bit more gas at that low speed, the noise is louder, like this is a spot where something is working harder to do whatever it is doing.

Man these cars are silly. Fubar.

[David T]

Tracking down noises can be extremely difficult. They may sound like they are coming from one place yet are actually coming from another. Check the upper right muffler bracket and go over the whole exhaust system. Check for exhaust manifold gasket leaks. Look at anything thin and metal like covers and such.

[DMC-81]

Hi Jonathan,

I would recommend verifying the level of the differential oil before driving it too much further, just in case it is the carrier bearings.

[Jonathan]

Tracking down noises can be extremely difficult. They may sound like they are coming from one place yet are actually coming from another. Check the upper right muffler bracket and go over the whole exhaust system. Check for exhaust manifold gasket leaks. Look at anything thin and metal like covers and such.

Thanks David. The cross over pipe cover that sits above it is one I'm going to get a better look at to see if something is rubbing.


Hi Jonathan,

I would recommend verifying the level of the differential oil before driving it too much further, just in case it is the carrier bearings.

I agree with you Dana. If it turns out to just be something annoying, but not damaging, so be it. But in the meantime, I like the reassurance of knowing where that oil level is. I may check the level, drain it and refill it anyway while I'm under there.

This is a photo of the drip tray I put under the car each day. I tend to clean it off before putting it back under after a drive.

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You can see on the left where I dripped brand new ATF as it is bright pink.

The clearish, yellow drip on the lower edge is brand new gear oil AKA rear differential fluid.

The top clearish, yellow drip is brand new engine oil, Castrol 20W50.

The long darker smear on the right side is what accumulated under the car while it dripped from about the rear cross member of the frame (slightly forward of that).

I did this little colour test because the drip oil doesn't look anything like the others. Granted the oil gets dark and gross while in the engine over time, but it still didn't really help me determine exactly what was dripping.

[DMCMW Dave]

Yeah - these can be hard to find. Almost easier to eliminate things:

- Wheel bearings generally cause a growl or vibration that can be made stronger or weaker by making a right or left turn. Not acceleration.
- Low differential fluid will cause gear whine way before the bearings get noisy. The whine will generally be only on acceleration or deceleration. Once you have it you're stuck with it, putting the oil back in won't fix it.
- I've seen vibration under acceleration caused by bad motor/trans mounts, i.e. on acceleration the engine actually rotates slightly opposite the wheel rotation direction. This kicks the transmission up against the frame, and you get the feel of the engine through the frame into the seat of your pants. You may have noticed that on EVERY car there is an area of the frame just forward of the transmission that looks like someone beat it with a hammer. I believe this is an assembly line "hack" to fix this problem. Never seen it documented but you see it on every car. This motion also kicks the other end of the engine down, which can make the exhaust hit things that it doesn't normally hit. Look for telltale marks on brackets.
- If you had described it as more of a miss, I'd suspect plugs/wires/cap/rotor. But that's not usually as subtle as you describe. It's not likely the fuel system since the fuel system isn't "timed". It could be a leaky injector seal, but that's pretty unusual to be had enough to feel it like that.

Question - When you say "on the gas" do you mean when acceleration only or do you feel it at a steady cruising speed?

Does it feel like a ignition miss (i.e. power cut out at engine RPM)? OR faster than that? To simulate an engine miss, take off a plug wire. Don't leave it like that for long, hard on the converter, but a few trips around the block won't hurt anything.

[Jonathan]

Thanks Dave.

I looked back at my notes (I keep a logbook, yea, dork, I know) and the first mention of the noise was 350 miles ago. At that time I thought it might have been related to taking a sharp turn. With that in mind, I thought it might have been the metal portion of the coolant pipe touching the bottom of my metal coolant reservoir. I put a piece of foam padding at the point where they might have touched, but the noise continued. So while I've heard it while turning, it's not as consistent as it is with accelerating.

The gear whine mention under acceleration or deceleration is the closest match to what I am hearing. I cannot get the noise to repeat if not actively pressing the gas pedal. The car can be in motion at any speed, but there's no noise if you aren't pressing the gas pedal (i.e. coasting while not pressing the gas). Further to that, it is much more evident when initially pressing on the gas and also at times when letting off the gas. However, when keeping a reasonably steady push on the gas pedal, the noise will fade away and stop.

So, yes, much more consistent with accelerating and decelerating than anything else. Almost to the point where I can't get it to repeat doing anything else. I'm not sure what a gear whine might sound like exactly compared to my own noise I'm hearing, but your description of under accelerating (and to a lessor extent decelerating) sure does fit.

For the motor and trans mounts, this could also be it as it's related to accelerating. My mounts are not in great shape. The motor mounts are rusty (like other brackets and fittings on my car have been before replacing them) and the rubber is of questionable condition. The trans mounts are less visible to see frequently, but looked more rusty than the motor ones on my car. I will definitely look closer for evidence of the pivoting like you described. I have not "felt" the noise though, not the seat of the pants variety anyway. It might be vibrating enough to feel, but it's not as obvious as the noise, so either I missed it or it's faint or not happening. Possible though still.

I would not think it is an engine miss. The engine seems powerful and okay when giving it gas. I had the shift computer rebuilt years ago and back then it had done the thing where it stayed in 1st gear and rev'ed at high RPM, but nothing like that for years since the upgrade. About the only sluggish feel I get is sometimes when first leaving my house going for a drive and it wants to hesitate slightly before changing into 2nd. That could be me not pressing the gas pedal down as much as I think I am or a cold engine and trans needing some warm-up time to get the fluids flowing (whatever that might mean). Hearing others describe missing engines doesn't sound like something my car is doing. I'd rate that as unlikely for the time being.

If it is a gear whine that isn't improved by adding differential fluid back in, what would have been damaged and what do you eventually need to do to correct it?

[opethmike]

Have you done this test with your motor mounts?

https://www.youtube.com/watch?v=m-kD9t-cnio

[DMC-81]

If it is a gear whine that isn't improved by adding differential fluid back in, what would have been damaged and what do you eventually need to do to correct it?

I'll leave that for Dave to answer, but since I recently had my gearbox apart, here's a picture of the carrier/conical roller bearing ( 103119 ) on a manual box to give a visual of the part in question.

Bearing
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Race
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[Jonathan]

Have you done this test with your motor mounts?

https://www.youtube.com/watch?v=m-kD9t-cnio

I haven't done this crow bar test yet Mike, no. Not sure why. I think when I saw it initially, it seemed like a good test but them got rebuked by someone I talked with. I don't have the car on a lift very often and wasn't sure I wanted to go at this while lying on the floor with it on jack stands. I did hear someone advise that poor looking rubber isn't necessarily a sure sign or bad mounts. It can be, but the real test is whether they are separating from the metal.

Here are a couple pics of mine. Driver's side anyway. Passenger is a little better. They don't look pretty, that much is obvious.

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I checked the rear differential oil level this afternoon. Pulled the fill port and felt no moisture to the touch anywhere on the threads or the short length my finger could get in there.

I then pulled the drain port and emptied what was in there. The fluid still looked pretty good both in colour and in smell. Gear oil doesn't smell very nice when new IMO though. 80W90 in there.

I got almost exactly 1 litre out, perhaps just a hair more. My notes from when I last changed it said I got out 1 litre back then and was able to put in about 1350 ml. The fill amount is probably a best guess as I recall spilling it all over the map trying to tip a bottle up when you're under there. Yea, fun.

I have not refilled it yet as I need to run out and get some more. Here is what it looked like underneath before draining. See the two drips on the low points of the rear differential casing? They are reddish and aren't at all like what accumulated when I drained the rear diff. Not as pink as new ATF, but too red I would think to be straight engine oil. How would ATF get up this far (or back) to give this drip a red colour? Am I forgetting something? I know my ATF cooler hoses are nearby, but I look at those somewhat regularly and they don't look like they are leaking.

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[Bitsyncmaster]

Get some small hose that fits in the fill hole. Then fill it from above the engine through the hose.

[Jonathan]

Get some small hose that fits in the fill hole. Then fill it from above the engine through the hose.

Good idea. Any trick to keeping the hose in the hole while you're above the engine and can't hold both things at the same time? I don't have a helper at my disposal.

[DMC-81]

That's good news that the differential wasn't starved of gear oil. Whew!

There are 2 SS heat shields above the crossover pipe. While you have the car elevated, it's a good time to check them for any looseness as you do your troubleshooting.

[DMC-81]

Good idea. Any trick to keeping the hose in the hole while you're above the engine and can't hold both things at the same time? I don't have a helper at my disposal.

I bought a gear oil pump at Advance Auto Parts ( you can probably find them at a Canadian equivalent) and it really makes the filling much easier. I made sure it would fit both quart and gallon bottles.
Here's a link:

https://shop.advanceautoparts.com/p/toughone-engine-fluid-oil-pump-w1139/9016678-p?c3ch=PLA&c3nid=9016678-P&c3apidt=23534110341&gclid=CjwKCAjwranNBRBhEiwASu908J6oA9IMyml8Ezcr4dlq INPSl5hcrpr8xHTUCnpHanKIc6og6sg8dhoCwccQAvD_BwE&gclsrc=aw.ds

[Bitsyncmaster]

Good idea. Any trick to keeping the hose in the hole while you're above the engine and can't hold both things at the same time? I don't have a helper at my disposal.

I had not problem just sticking it in a few inches. I'm talking about the hose so no wise cracks.:hihi:

[DMCMW Dave]

If it is a gear whine that isn't improved by adding differential fluid back in, what would have been damaged and what do you eventually need to do to correct it?

Replace the differential. it is not really practical to replace just the gears. This is not as bad as it sounds since used ones are pretty readily available, this is the only failure. People sometimes replace an entire faulty automatic trans due to clutch or hub failure, but the differential (a completely separate part) is still in fine condition and available for this sort of repair.

The damage is that you've worn the face (case) hardening off the surface of the hypoid gears, so they don't mesh properly any more and now make noise. Damage is done, and other than the noise there really isn't any harm in continuing to drive it like that for a long time.

It really is a gear whine, not a rumble or flutter. Sorry - sounds/feels are hard to put into typed words.

[Jonathan]

I bought a gear oil pump at Advance Auto Parts ( you can probably find them at a Canadian equivalent) and it really makes the filling much easier. I made sure it would fit both quart and gallon bottles.
Here's a link:

https://shop.advanceautoparts.com/p/toughone-engine-fluid-oil-pump-w1139/9016678-p?c3ch=PLA&c3nid=9016678-P&c3apidt=23534110341&gclid=CjwKCAjwranNBRBhEiwASu908J6oA9IMyml8Ezcr4dlq INPSl5hcrpr8xHTUCnpHanKIc6og6sg8dhoCwccQAvD_BwE&gclsrc=aw.ds


I had not problem just sticking it in a few inches. I'm talking about the hose so no wise cracks.:hihi:

Thanks for the tip. (Eeeek!, lol, aren't I punny!) I found something similar to that gear oil pump locally and it should work just fine.


Replace the differential. it is not really practical to replace just the gears. This is not as bad as it sounds since used ones are pretty readily available, this is the only failure. People sometimes replace an entire faulty automatic trans due to clutch or hub failure, but the differential (a completely separate part) is still in fine condition and available for this sort of repair.

The damage is that you've worn the face (case) hardening off the surface of the hypoid gears, so they don't mesh properly any more and now make noise. Damage is done, and other than the noise there really isn't any harm in continuing to drive it like that for a long time.

It really is a gear whine, not a rumble or flutter. Sorry - sounds/feels are hard to put into typed words.

Once I get the gear oil refilled and other inspections done while it's in the air, I'll take it for a drive and record the audio (or video plus audio if my dashcam will pick up the sound well enough). I'll post that here so it's not so ambiguous as to what the sound is. Agreed on sounds "sounding" different when typed from one guy to another.

Thanks for the help and advice so far. Really appreciate it!

[Jonathan]

Ok, got the rear differential fluid refilled. Took about 1.4 litres before it was starting to slowly drip out the bottom edge of the fill port.

Took the car for a ride and thought it might have done the trick, but alas, not so lucky. It was doing the noise again, maybe even more so than before.

Here's the audio I took from a 15 minute drive. I edited this down to about 1 and a half minutes. This was when I closed my window, so just cabin noise. I think you''ll be able to make out the vibration sound I speak of. Again, only happens when actively pressing the gas and only happens when the car is in motion, i.e. doesn't make any noise when parked and the engine is running.

(I had my phone sitting on the middle armrest right in front of the coin tray while it was recording the audio)


https://www.youtube.com/watch?v=xGmCqwDYS8s&feature=youtu.be

[DMCMW Dave]

Differential noise is a higher-pitched whine. What kind of tires do you have on the car, i.e. brand/size/miles?

[DMC5180]

That actually does sound like a vibrating heat shield. Like the one attached to the crossover pipe. Its not gear whine.

[opethmike]

Cat heat shield? Heat shield on the cross-over pipe? Check those.

[Jonathan]

Differential noise is a higher-pitched whine. What kind of tires do you have on the car, i.e. brand/size/miles?

Tires are Dunlop GT Qualifier (on all four). Standard DeLorean sizes. Dates codes are from late 2006. Been on the car the entire time I've owned it (Fall 2007). About 12,500 miles that I have driven on them and not likely much more than that since they were new (probably bought by place that was selling the car then).

What noise ideas come to mind with respect to the tires?


That actually does sound like a vibrating heat shield. Like the one attached to the crossover pipe. Its not gear whine.


Cat heat shield? Heat shield on the cross-over pipe? Check those.

Glad to hear the consensus isn't gear whine. When I listen to that audio myself (on the computer and not while driving), it almost sounds like one of those idiotic fast and furious attempts and the guy's exhaust is rattling up against something. I'm leaning towards the crossover pipe heatshield too and will check it in the morning. Wanted to let the engine get cold tonight before reaching in and around there making sure things are secure.

[DMCMW Dave]

I asked about tires because some tires (especially the older blockier treads, and Goodyears) tend to get noisy with age. But that wouldn't change with acceleration/deceleration, only road speed.

Heat shield is, on paper, hard to fix "properly" and a common rusty-car problem. Luckily it's easy to fix "improperly" with a couple of well-placed hose clamps.

The heat shield is attached the crossover pipe in two pieces with several bolts that are, at this point, welded into bungs on the crossover pipe. You'd have to remove the pipe for access (it is held to the manifolds and converter with a few more guaranteed to break rusty bolts/studs). Rust isn't always an issue, but on your particular car, and most northern climate cars, it will be.

I couldn't tell much from the audio file, but it occurs to me that you may be hearing the very early beginnings of exhaust manifold gasket failure. In the begging they are only noisy on acceleration, but won't be noisy revving the engine with no load. It will get worse over time. In that case, at some point you'll have the crossover off the car. This is commonly misdiagnosed as noisy valve rockers BTW.

[DMC-81]

I asked about tires because some tires (especially the older blockier treads, and Goodyears) tend to get noisy with age. But that wouldn't change with acceleration/deceleration, only road speed.

Heat shield is, on paper, hard to fix "properly" and a common rusty-car problem. Luckily it's easy to fix "improperly" with a couple of well-placed hose clamps.

The heat shield is attached the crossover pipe in two pieces with several bolts that are, at this point, welded into bungs on the crossover pipe. You'd have to remove the pipe for access (it is held to the manifolds and converter with a few more guaranteed to break rusty bolts/studs). Rust isn't always an issue, but on your particular car, and most northern climate cars, it will be.

I couldn't tell much from the audio file, but it occurs to me that you may be hearing the very early beginnings of exhaust manifold gasket failure. In the begging they are only noisy on acceleration, but won't be noisy revving the engine with no load. It will get worse over time. In that case, at some point you'll have the crossover off the car. This is commonly misdiagnosed as noisy valve rockers BTW.

I agree with Dave. As you are checking the crossover pipe, here's a picture of it out of the car and taken apart to give a visual of what you are checking for. I found that the 4 bolts got more rusty than the rest of the pipe. I think if you wiggle the shields a bit on the car, and you are able to move them, that will point to one or more failed/degraded bolts.

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When I restored this pipe, I had to use heat, wax, and rust penetrant to gradually coax the bolts out, and that is on a Southern car.

I also agree on the possible sound of failed exhaust gaskets. Mine made a fluttering sound, and got worse over time. When I got the manifolds off, I found 3 of 6 ports were leaking. I saw black soot around the leaky gaskets, and/or a rusty/disintegrated gasket.

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[Jonathan]

I found the source of the noise.

It was in fact the crossover pipe heatshield on top. And specifically, it was the passenger side half that had one of those two bolts sheared off at the head. Thanks for the suggestions and pictures. The only thing remaining was a tiny bit of the threaded portion, but enough to keep the washer in place. Sort of. The washer wasn't tightened down onto anything, but couldn't just fall off because a bit of the broken bolt had stopped it from coming out on its own. It was plenty loose enough to rattle though... every time you hit the gas.

I got the washer out of there and put a hose clamp on for the time being. That is not a nice area to gain access to from above, so once I get some time to get at it from underneath properly, I'll put a couple hose clamps on and make sure they're good and tight and well centred. In the meantime, it stopped the vibration noise. I went out for about a 30 mile drive and the car drove real nice.

I'd say it was a big relief to get it sorted out, but I wasn't really all that thrilled about it when I finally tracked it down. I probably just muttered asshole to the car as I shut the light off in the garage and went inside.

[DMCMW Dave]

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That's a really good picture of what to look for when the exhaust starts getting noisy. You'll see black soot marks like this on the bad ones, and you'll often see the gasket starting to fall out, indicated by the unused holes no longer lining up.

[DMC5180]

I found the source of the noise.

It was in fact the crossover pipe heatshield on top. And specifically, it was the passenger side half that had one of those two bolts sheared off at the head. Thanks for the suggestions and pictures. The only thing remaining was a tiny bit of the threaded portion, but enough to keep the washer in place. Sort of. The washer wasn't tightened down onto anything, but couldn't just fall off because a bit of the broken bolt had stopped it from coming out on its own. It was plenty loose enough to rattle though... every time you hit the gas.

I got the washer out of there and put a hose clamp on for the time being. That is not a nice area to gain access to from above, so once I get some time to get at it from underneath properly, I'll put a couple hose clamps on and make sure they're good and tight and well centred. In the meantime, it stopped the vibration noise. I went out for about a 30 mile drive and the car drove real nice.

I'd say it was a big relief to get it sorted out, but I wasn't really all that thrilled about it when I finally tracked it down. I probably just muttered asshole to the car as I shut the light off in the garage and went inside.

[emoji1303]

[NckT]

At least it'll be a cheap fix!

[DMC-81]

That's great news Jonathan! :thumbup: