This 2002 X5 has developed a very distinct, consistent vibration at idle in drive or reverse with foot on brake holding the car. Goes away and performs smoothly as soon as you accelerate or select neutral/park. What could it be?

I have the same problem on an 03 X5 3.0 all wheel drive that is driving me nuts. I just replaced the front drive axles and a power steering line and some new belts and the owner say's the vibration was not there before. I have re-checked all my work and even replaced some motor mounts with no avail. This X5 has approx. 60K miles.
Any one else deal with this?
Thanks for any input.

Transmission...
vacuum leak...
I know nothing and prove it daily...

Heated seats on? More pronounced the colder it is?