the drive shaft can get out of balance. THere are companies that specialize in rebuilding and rebalancing the drive shafts.

Conventional wisdom is that this should never have to be done unless the drive shaft has been damaged....

__________________
Mark Herzig
1995 E300D 153K
1985 300D 142K (sold)
1979 450SL 122 miles (sold)
1992 500E 127K (sold)
1987 300SDL 132K (sold)
1986 300E 161K (sold)