I have nothing to add, other than I know the bad feeling of not being able to diagnose the vibration. Mine tends to vibrate on acceleration, under medium to heavier torque.....but it doesn't happen all the time. It seems to happen more right before the 2-3 gear shift approximately 35-40 mph. It's frustating. I've taken it to 2 MB mechanics who looked over the driveline on the lift (one while it was idling) and they don't have a definitive answer. I'm afraid of throwing money into it and getting no improvement. I did have the transmission mount changed and there was no improvement. If you guys read my posts, I've had an issue with my car being sluggish, but I always could depend on it being quiet and smooth. Now with the whining noise and the vibration (for a year now with the vibration) it's been really disappointing. I'm waiting on pins and needles to see if you find an answer to the vibration at least, Brian. Good luck.

It does seems that running it on a dyno (that someone suggested in another post) and seeing what the driveline and wheels does when it vibrates would be the most direct way of seeing the problem.

"MB God", Steve Brotherton, have any input?