The motor mount used on W124 and W201 has a built-in engine shock absorber which is filled with ethylene glycol. If the bottom of the metal cover and the subframe is less than 13 mm, replace the mount.

The thump noise you heard may be due to the fact that one side of the engine is momentarily jumping up and down against the subframe. When you start pressing the gas pedal, the defective motor mount is not able to hold down the engine against the torque created by the engine.


David