Hi All:

I have a 2005 CTS-V (LS6) with approximately 120K miles.
For the last 5K miles or so I have noticed a driveline vibration that has been very difficult to isolate. This began (coincidentally or not) with a right rear wheel bearing that needed replacement. The rear diff noise vanished with the new bearing but the driveline vibration remains.

It comes on at approximately 15-20 MPH, recedes and then comes on again at approximately 40-45 MPH. It is more noticeble when lifting off and is virtually gone by 60-65MPH.

I have naturally ruled out wheel balance issues. The clutch / pressure plate is likely original although it is possible that it has 100K miles since I purchased the vehicle at 24K and the rear differential had been replaced by Cadillac at approximately 19K.

A local tuner seens to think it could be an engine balance issue. Aside from the vibration the car runs great. There has been no loss in mileage or performance. The clutch does not slip or chatter. The engine and trans mounts are all in good condition as is the drivesharft and u joints.

Has anyone runs into this? The vibration is driving me nuts.

Thanks, Paul