My 85 300D has a very high pitch whine/whistle (no so much a squeal) that seems to be coming from around the right rear wheel well and can be heard best with my head in the trunk. Here are the particulars:

*It usually starts a minute or two after startup
*it is a solid tone that does NOT fluctuate with speed/RPM
*It stays constant at idle, matter of fact it will do it without ever moving
*When engine is shut off the sound remains but trails off/winds down after about 10 seconds.

I'm thinking it might be a small vacuum leak making a whistling sound but not sure. Anybody have a clue?

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'85 300D

sounds like a vac leak. isn't the fuel door vac pod right in that area? check it and it's connection.

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Mark
1983 300TD Wagon
Even a broken watch is right twice a day

You can also disconnect the vac lock triple tree in the engine bay for diagnostic purposes. With no air being sucked through the system it should stop whining if vac leak is the problem.

aha this might be the problem with my door locks since i have the same noise in my trunk

High pitch whine from trunk

Did you buy this car from a mobster?

I used to have a high pitched screech from the righ hand side of the front passenger seating area....and it only happened at over 80 mph, and only when my wife was riding in the car......I'm single again

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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)

It sure sounds like the fuel door vacuum actuator to me. Does your door loks system hold vacuum after the car has been shut off? The actuator is behind the plastic panels inside the trunk, just to the rear of the fuel filler.

Yep, for about 10 seconds, which is about as long as the noise lasts after shut down. I think you and the others are onto something. I'll dig in there tomorrow when I have time and report back.
Thanks for the feedback (even the smart a** replies)

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'85 300D