bad rattle when cold

[bieny]

hello everyone,
got a strange rattle noise when i start the engine, you cant hear it at idle but its really bad when you blip the throttle. it goes away after about 45 secs - 1 min but will be back is the engine is off for more than 10 mins.
the noise comes from the rear left (turbo) side of the engine and is to loud/deep to be a tappet.
its somewhere in between a tappet sound and the manifold blowing. (its really hard to describe a sound!)
I think it might be the cam chain tensioner? are these a common problem or could the oil pump be at fault?

all the threads about 'rattles' say its normal but this definetly is a bad noise!

any help would be much appriciated

cheers

[bieny]

well ive changed the cam chain tensioner on audis recomendation but the noise is still there!