I would guess.
The driveshaft center bearing, and support could be the cause.. Apparently a fairly common failure at over 100K miles..
I posted a "how to" article on replacing them a while back on a 300sel..
89 300SEL Money Pit
92 Blown Buick Ultra Pimpmobile 220K and adding 1K per week
88 Wagoneer Slightly modified (Not for soccer moms)
04 Kia Sedona with every option... NICE