Your current pump is on its way out. There are many things mentioned above that can cause a noisy pump, but it can very well be the pump itself. My old pump did the same thing...for over a year! whenever it got hot it hummed and if I kept driving, it would eventually stop altogether. I tried all the fixes, spring in the pickup hose, fresh gas when it made noise, making sure the pickup was not twisting due to improper pump reassembled, etc. Once during a fairly warm day while going over a mountain, she started groaning and finally crapped out. After it cooled down a bit it performed perfectly. I have previously dismissed the pump being the culprit since it always worked fine shortly after and I had been going on advice about this common problem being related to other things. 2 years ago, I finally realized this could be the pump itself and replaced with a DMC pump, (not hervey's junk) and its been fine ever since. I have even driven this car in 107 degree weather in stop and go traffic with no humming or noise.
Do concours judges open up the fuel system to check?