i would suggest checking any and all suspension bushings or subframe bushings,
If you still have it when the transmission is in neutral, and it's not the wheels, then it's related to the drive shaft or differential.
I would also suggest checking the wheel bearings just to rule them out as well as a bad wheel bearing can also have a high pitched sound.
does the noise change if there is a heavy load in the rear of the car? if so then i'd focus on bushings
Its, not the bearings, it still happens in neutral, replaced bad front drive shaft, NOT the rear drive shaft so it's got to be the differential I guess
Would it be possible for you to post a driving video with the car making the noise you describe? That might help us to be able to help you identify the noise and come up with a diagnosis.
hi, i went down this same rat hole with my 300d, the dealership nor and independent mb shop could figure it out, replaced the axles, differential, complete drives shaft w bearing and both rear axle bearings, sub frame bushings and diff mount. the only thing left is the 42 year old trailing arm bushings. i found when i had a lot of weight in the trunk the noise would go away, the other thing that is pointing to the trailing arm bushings is the position of the rear wheels in relation to the wheel arch, its obvious one side is not tracking the same as the other side. i'd still recommend loading up the rear of the car to change the suspension angles and see if the noise goes away or changes.
Had the car up on a lift and got the same vibration at speed. Checked all bushings, axles, half shaft. Differential was solid and I still had the vibration. Bizarre
hi, i did the same with my 300d, before you spend a bunch of money on rotating parts check your bushings. trailing arm , subframe. also. load up the rear end so it sags and then drive the car, if the noise changes or goes away bushings are suspect
Had a load of Duraflame logs in the back yesterday so it was weighted down, no effect on the harmonic vibration. The only thing that make sense at this point are the half shafts, I'm struggling whether to replace those or move on and sell the car. If I could be assured that the axels are the problem I'd do it but it's an expensive roll of the dice.
on your model car can you swap the axles left to right to see if there is a change in vibration? if so the folks at this link may be able to inspect and possibly rebuild yours or sell you a good used pair https://www.dieselmercedes.com/productslist.asp
interesting idea thank you.