spcds1529

I own a 2016 E-350 4matic 3.5 with 94,000 miles. It has been a great car and I would like to keep it as long as possible. The transmission was serviced by Mercedes specialist when recommended by the manufacturer. It is my wife's car so I do not drive it very often. I drove it recently on a long trip and noticed a very faint whine when I let off the accelerator. The whine goes away when the accelerator is pressed again. It is so faint my wife says she cannot hear it. I do not notice the sound when I'm driving around town. The transmission is in E mode, I do not know if it is the same in S mode. Is this sound normal? Thanks for any help anyone can provide.

S-Prihadi

Usually whine under load could also be the differential. Yours is 4-matic, so you got front and rear differential.
If you can find a road where it has one side a sound barrier or a wall, opening the window when driving and to re-confirm the whine is good with such walls as the reflection is strong from
such walls.

Arrie

You could use the paddle shifters and change gear down to see if the whine changes. If it does, then it is an indication of wear on the gear it makes the noise with or the shaft bearing the gear runs on inside the gear box. Change in whine would tell the problem is inside the gear box.

If it does not change then it comes from one of the differentials or the transfer case that includes the center differential.

MBNUT1

Mine does the same I think that it is rear differential whine as I have had my front differential replaced with a lower mileage unit and the transfer case rebuilt.

W205C43PFL

Yes it is the rear diff, the whine is common across W222, W205, W213 etc.
https://mbworld.org/forums/c450-c43-...-thoughts.html
https://mbworld.org/forums/s63-amg-s...ine-noise.html
https://mbworld.org/forums/s-class-w...-replaced.html
https://mbworld.org/forums/e-class-w...-coasting.html

nc211

I would change the diff gear oil, especially the back. The 4matic on this car is fixed and rear-bias, meaning the rear takes the brunt of the torque all the time. While you at it though, and while the car is on the rack, walk up to the front passenger side and use a flashlight and look down the plastic tube of the driveshaft to the front diff and see if it has any leaks. They will leak on the front because of a seal that does wear out. If it's leaking, then you might as well change that gear oil too, because that drive shaft is coming out regardless to replace the little seal. Fun fact on our cars on the front diff - you can drain it easily, but there is no fill plug. You have to pull the front passenger side axle out to fill it back up. #winning, said nobody with a 6th grade engineering background...

W205C43PFL

Appreciate you chiming in and sharing your experience from an engineering perspective, can't go wrong with doing fluid changes for sure as a first step!

MBNUT1

I know, Just how stupid is that design?

Quint22

You can if you get an adaptor and pump the oil in from the drain plug. Not ideal obviously but doable.