Car has a thump clunk sound when letting off gas pedal
Some Mercedes-Benz cars with 4Matic such as ML, GL, R, S, E Class (or any car with 4wd) may develop a clunk, thump when you let go of the gas pedal. This can happen at slow and high speeds and even under normal acceleration.
At first, you may think that the issue is a bad engine mount. These symptoms are commonly experienced when the engine mount fails but engine mounts tend to show these symptoms under hard acceleration only.
Our client described the problem as a wired thump when letting off the gas. It happened almost every time. The clunk felt uncomfortable and would happen even when you are easing off the gas pedal. If you normally press then release the gas pedal and you feel the thump, you know the problem is not an engine mount.
These symptoms were caused by a bad front differential bushing. The bushing shown in the picture will crack and create too much free play for the differential. To verify jack up the car. Grab the end of the front differential (carrier) and check for play.
If there is any play or cracks, the rubber bushings should be replaced.
Also visually inpect the rest of the front differential bushings for cracks. There are three bushings. The rearmost bushing seems to fail most often.