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.
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.
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 inspect the rest of the front differential bushings for cracks. There are three bushings.
The rearmost bushing seems to fail most often.
Another common issue that causes similar symptoms is a broken engine or transmission mount.