My M6 had the same symptoms. This is caused by the accumulators losing their charge. This creates the situation when the ride-height sensor senses a low condition, the pump is actuated to raise the ride-height. Since the accumulators have no N charge, the pump moves the rear of the car at to fast a rate, overshooting the proper height. After replacing my bad accumulators, the rear of the car moved at 1/10th the rate it previously moved at, stopping at the proper height.