A vibration felt through the center floor of the vehicle can be caused by cracked and/or shredded driveshaft flex discs, resulting in excessive driveshaft movement. If not repaired, damage to the driveshaft center support bearing, transmission, or differential can occur.Google+
Car Problem Reports
Mercedes-Benz E320 Cracked Driveshaft Flex Discs May Cause Driveshaft Movement/Vibration
Mercedes-Benz E320 Problem
Average Mileage: 152,500 mi (92,000 mi - 260,000 mi)
same as described. vibration rear center. around 37 mph feels like running over washboard or rumble strips
Vibration transmitted through the vehicle floor just behind the front seats. Had tires checked and balanced. Confirmed that all exhaust hangers were solid and connected.
Visitor, 1999 Mercedes-Benz E320, 260,000 mi
Vibration detected at fast start.