I saw a clean 560SEL in the paper w/ 150k miles. Saw and test drove it. Note: Car drove very good. Engine is in perfect shape. Tranny shifted good in all gears even reverse was good but when I was in reverse I heard like a louder than usual whine from the tranny. When in forward gears there is no whine? Could this be from the rear end? When travelling, the rear end sounds quiet. I dont know what that noise is. Tranny shifts fine and engages correctly? Also the tranny fluid needs to be replaced. If i replace it then would or could this noise go away?