If I manually select gears 1 or 2 (a bit in 3, though over 30mph road noise would drown it out anyway) on my gearbox, then I get a whine on the overrun/ under engine braking. Fairly high pitched. This happens in Drive too, but is most noticeable in the manual selections as the box cannot shift to neutral so the gears are constantly in mesh. I know that in a manual gearbox this is due to the back of the gear teeth not being machined or worn in in the same way as the side of the tooth normally in mesh when accelerating. Do other members 722.6 boxes make a similar sound when locked in a low gear or is mine clapped out? I did have a go in another C250TD with a higher mileage than mine and it made similar whiney noises on the overrun in the lower gears. Both his and my car have been doing it for ages (I think since before I got the car 20k miles ago) so if it is something letting go then it is taking its time? The other idea I had was maybe there's a worn thrust bearing, and when the load is transferred the other way down the geartrain on the overfun, it puts pressure on the worn bearing. But then why would the thrust bearing for the overrun direction be worn anyway, seeing as it is the one taking the brunt of acceleration which should surely wear first?