The early generations need the center bearing replaced at 70,000 miles.
The dealers will want to replace the drive line, but there is an alternative available from
EPS. (and others)
 Porsche Cayenne Drive Shaft Center Support Bearing - Cardan Shaft - Propshaft Replacement Repair — European Parts Solution
FWIW, I got 40,000 racecar towing miles up and down the east coast with my V6 - never let me down.
Bill K