vibration while in drive or reverse but not moving.

I have 2001 X5 3.0 that has vibration when in drive or reverse but not moving. I have replaced motor mounts, replaced all suspension components, front axels rebuilt, changed gear lube in the differntials, new serp belts, spark plugs. I have checked the transfer case mount and it is in good condition. I am stumped and can not figure out where the vibration is coming from. In neutral the vibration is not present. Does anyone have any ideas or experience with this? What could be the source of this annoying vibration?