I purchased an '08 GTS Cayenne a few months ago, and have noticed a vibration from under the seat. My dealer states its the rims (because he wants to sell me some rims), however, I have been researching and some owners state the "cardane shaft" may be out of balance. Any suggestions? It happens about 72 mph. Thanks,

 

Take the truck to a good tire shop and ask them to balance the rims/tires - if you can find it - a Hunter Road-Force balancer is the state of the art right now. If it still vibrates - it might be the "cardan" shaft - mebbe.

 

Think the problem come from the wheel, front, and you just have to rebalance them

 

I too have a drivetrain bzzzzzzz vibration that starts at about 78MPH up. Re-balanced all 4 wheels - found tha the front right was off a little. I was hopeful that this would fix it - but it didnt. Vibration is "faster" (if that makes sense) than wheel speed. I'm now 90% certain it is the bearing in the driveline - which is a known weak-link in the Cayenne's.