Mine has done it for the last 15k.. Unfortunately I think it is a characteristic of the gear box..
Try putting it in manual and holding it in 3rd or 4th over bumps it tends not to do it.
Im on my second gear box. Was quiet after the change back in January rattles again now. Learning to live with it. Seems at its worst when the gear box is not under load. Qudible clunks when changing up and down though.
B


