High pitched noise from alternator

[DaraSue]

Last night I heard a weird noise that seemed to be coming from the alternator. It was about 15 minutes after I'd turned the car off. Keys were still in the ignition but the noise continued after I took them out. It was a high-pitched whine, sounded kind of like tinnitus or the electrical field noise you hear behind a CRT tv that's on mute.

I noticed this same noise last year when I was having the issue with the throttle sticking and thought it might have had something to do with the engine revving at 5000+ rpm, but this was after a normal drive home from work that never went much above 3000. I can't say with 100% certainty that it hasn't been happening the whole time because I'm not usually in the garage with the door closed at night after shutdown. When it happened last year I asked a mechanic friend about it and he didn't think there was any way the alternator could be making noise with the engine off but it definitely sounded like that's where it was coming from (I didn't hear it at all inside the car). Last time it went away when I switched the battery cutoff off.

Has anybody ever heard of anything like this?

This is the alternator: IMG_20200612_091448099.jpg IMG_20200612_091510893.jpgIMG_20200612_091532106.jpg

The guy who sold me the car swears it's a 200 amp that came from DPI but they don't currently sell one with that rating and I can't find any DeLorean vendor who does. (It was installed around 2016.) Another mechanic friend of my neighbor looked at it and said it looked like a Chevy alternator. Does anyone recognize it?

I had taken the car to Autozone to get it tested when all this happened last year and they said it had a bad voltage regulator but the car has been starting and running fine this whole time (volt meter stays around 13). How likely is it that that's actually the case? If it actually is a 200 amp, is that too much for this system? I'm not running any insane aftermarket electrical stuff.

[dmcnc]

I've had that same issue with the GM alternators (2 of them); like a tube TV high frequency noise. The noise came with a parasitic drain on both alternators so you may want to check for that.

[Delorean Industries]

Definitely not one of ours. All of our units have black powder-coated finished fans, billet bracket, billet pulley, and 5/16 bolt instead of the 10mm. This is Hervey's unit for sure.

[DaraSue]

Thanks, guys. It does kind of look like the ones Hervey had on his site back in the day. https://web.archive.org/web/20160326...ternators.html

I've got a DuraLast from Autozone that I bought just in case, might swap it out and take the current one to a rebuild shop and see what they say.

dmcnc - when you say there was a parasitic drain, what symptoms were you having? Low voltage, battery drain?

[Michael]

Check the charge rate. I would not be surprised to hear it's burnt up.

[dmcnc]

Battery drain. BTW - you could purchase something like this and just swap the front case (the aluminum shell facing the pulley), making it a direct fit.

https://www.amazon.com/DB-Electrical.../dp/B007XUI4MG
https://www.ebay.com/itm/200-AMP-811...Make%3APontiac

when you say there was a parasitic drain, what symptoms were you having? Low voltage, battery drain?

[gluaisrothaii]

My DMC alternator has the whine and parasitic drain. Replaced it and the second DMC unit does the same. Not every time, and what I have found is that if I turn the ignition back on for a couple seconds after shutting down, the whine stops and there is no parasitic drain. Can’t really figure out why that works but it does