renault laguna 1800 16 valve 2002 new shape?

could any one give me some advice got a laguna and its devoloped a noise sounds like under the rockercover, stripped it down checked cams etc, changed hydraulic tappets and rocker rollers, new timing belt kit, and the noise is still there, the noise is only there when the engine warms up and the easiest way to describe it, it sounds like a diesel, take the revs from 800 on tick over to a 1000 and the noise goes, also removed sump checked pump and pick pipe, refitted sump and changed oil and filter, still there any ideas regards lee