Noisy Gearbox

[wherzmespana]

Help - I have a 6 speed box out of, what the previous owner told me, a GT2. The last serial numbers on the box are 964?? At idle there is a fairly loud knocking from the back end of the box - it doesn't sound right but shows no signs at all of failing/causing problems. Anyone got any ideas or alternatively know anyone that can do a decent rebuild in the Cheshire area?? Thanks