Our 82 240D did that too. We thought there
was something wrong with the transmission. It turns out that the engine mount on the passenger side was fully collapsed. When you accelerate, the torque of the engine causes the metal bracket if the engine support to rub the chassis. It was a groan. After installing new mounts the problem disappeared. Just a thought.
[This message has been edited by DieselGuy (edited 09-28-2000).]