My GS400 is doing the same thing as TGONDER, the OP. I hear a clunk from the rear end area upon quick take off and also feel a loose kind of clunk feel coming from the rear when i stomp it from a cruising speed. It is also noticeable when im holding the brakes firmly and I shift from drive to reverse and drive again.
No braking noise
No moaning noise
Also dont notice the engine moving a whole lot with the hood up, brakes held and shifting back and forth from drive to reverse.

Im guessing either the diff mounts or the driveshaft to pinion bushing. But i want someone under my car when I recreate the noise. Havent had a chance to do that yet.

 

So on every single forum i read about this clunk. Yes no moanning or clunk with brake. Only when putting foot on gas pedal hard from a stand still. And from no gas in gear to a stomp on gas then clunk. Please does anyone come back here and say what they fixed to fix this problem

 

My both lower motor mounts are bad just got a
quote from a shop $670 to replace both bottom mounts and tranny mount
does the price seem right?