A vibration felt through the center floor of the vehicle can be caused by driveshaft flex discs, which crack and shred, causing excessive driveshaft movement. Not repairing these can cause damage to the driveshaft center support bearing, or, in the worst case scenario, damage to the transmission or differential.Google+
Car Problem Reports
Mercedes-Benz CLK500 Cracked Driveshaft Flex Discs May Cause Driveshaft Movement/Vibration
Mercedes-Benz CLK500 Problem
Visitor, 2003 Mercedes-Benz CLK500, 39,850 mi
Slight vibration and loud noise like a rumble strip at 40 mph. Goes away if you back off the accelerator. Cracked front flex disc. Front and rear discs replaced with new parts. Car now runs fine.