Freelander TD4 odd noise

Hi I have a 2002 TD4 Freelander which runs great but sounds rough. The noise is difficult to describe but it sounds like a dry chain being dragged across a steel pipe. The noise seems not to alter in pitch whether the engine is on tick over or high rev's. Any help would be much appreciated.

Regards
Tunnel1a

Welcome. Ask yer questions in the Freelander section if yer need help.