Weird drivetrain movement

[Said Ghazzawi]

Hello
I have a 2011 E350 and im facing a weird problem
If i put the car in Park or Neutral and rev the engine, the drivetrain will make a weird clunk and thump when the rpm is going back down
I changed the engine and transmission mounts and the clunk reduced but did not go away.
The mechanic says its normal on all these models but im not sure
Any ideas?
Thank you

 

[Uncle Benz]

If it improved with new mountings I'd probably inspect the exhaust system next.