noisy 300tdi-engine

Hi folks, being a 60 petrolhead I think I know quite a bit about engines in practice and theory. My M-reg Disco 300 tdi is my first diesel though. I try not to bore you with the full story by now about this 136kmiles engine. Better step by step to get to the bottom of the problem. So, here is my first one:
Engine is clattering loud when started cold.This gets a bit better after a few seconds of oilpressure build-up. This noise is not dependent on load, but disappeares almost completely after releasing the accel pedal=overrun. Question: could this possibly any of the components of the valvetrain,i.e. camshaft,camshaftbearings,followers,rollers,excessive tappet clearance? Is any valvetrain noise dependant of load in a diesel like the 300tdi?(In petrolengines never,as far as I know) Cheers,reinhold