Thread: small noise

Hi all, My D2 td5 has developed a small ticking sound coming from the gear box area.(manual box ) At first I thought it might be the fuel regulator as its leaking and needs replacing. But I've noticed that it only happens in 4th and 5th gears. It only happens when under power( not when coasting ) and gets faster with increase of speed. It also changes depending on which gear.
Has anyone else had this same noise ? What did you do or what is the cause ?
Thanks.