Hi Sonya,
The 500 is a decent engine, but the build quality of our ML series are not that great.
The transmission fluid needs to be changed, the software updated, and possibly new shift solenoids/valve body to stop the transmission clunking. The fluid change will not evidently work the first time because the torque converter on these has no drain hole. I change 5 quarts, run it, change 5 quarts again, run it again, and finally do a full change. This lets me know I get most of the old fluid out.
The valve body and shift solenoids are known to cause the clunk, it is just hard shifting, but, if this transmission was already updated, you could have motor mount or transmission mount issues.
Having to press the gas in reverse just to get the vehicle to move should not be happening, and the throttle position sensor and gas pedal may not be synchronized.
Before you drive next, turn the key to ON, but don't start the engine. Hold the gas pedal down and listen for a small electric motor to make some noise back and forth. It is right below the windshield, under the hood.
Lastly, the nudging forward may be related to the gas pedal/throttle body synchronization, or you may have an issue with your brakes.
For the drive-shaft, a little whine is normal, but if you are getting chirping or clunking, change the universal joints.
Let me know any questions you have, and here is a link if you would like shop recommendations: http://repairpal.com/mercedes-benz-within-10-miles-of-medford-massachusetts-02153
