Lukas
It wouldn't hurt to drain the transmission oil and examine the drain plug. The drain plug is magnetic and will capture any steel bits worn from the gears. It would also
help to stain the oil through a fine screen filter as you drain. This may show any other bits worn  that are not magnetic like brass from the syncros. It would be best
if the transmission oil was warm/hot when you drain it so a drive of a few miles would probably raise the temperature enough.
Here's hoping that you don't find a Christmas tree standing on your drain plug magnet.
Larry
PS. before you drain the oil make sure that the filler plug will remove easily. Better still remove it when draining. When refilling, use a good quality synthetic gear
oil.

> Dear ALL
> I had a good look and listen under the bus. The ratteling is coming from the
> gearbox at the rear end.
> I checked, there is Oil in it..
> The ratteling is there as soon as the engine idels and goes away once the
> clutch is pressed.
> What should I do next.
> Lukas