Driveshaft get disconnected and reconnected lately?

Flex discs getting worn?... replace before those blow!

A wheel is out of balance? ...threw a weight, sudden change

Flex plate on the back of the engine? ..maybe.

Does it happen when coasting in neutral too? Try to determine if it's rolling gear, or engine / tranny related.

..under load, or little load?

A wheel bearing?

__________________
Cheers!
Scott McPhee

1987 300D