I have '99 M3 mine does it too, but after UUC TME haven't happen since. "Since the transmission is connected to the back of the engine, it is the engine which is doing the twisting when one accelerates or decelerates (engine braking). Since the engine has it's own mounts (motor mounts), the transmission also has it's own. Whereas some movement is expected, too much movement will cause the transmission to become misaligned with the interior of the car. When the transmission is not in the same position, it may lead "miss-shifting" (aka shifting into the incorrect gear)." http://www.uucmotorwerks.com/