For the last few months I've had a very strange noise from the engine when cold, and it seems to be getting louder. It completely disappears after about 3 to 5 minutes, i.e. when the engine warms up. It is a cross between a whinning noise and a tapping noise, and is getting embarrasing. At first I thought it was the connection between the turbo and the down pipe, but I've replaced this gasket and tightened this, and still happening. The revs seem fine when cold or hot, and there seems to be no difference to performance once it is hot.
If I leave the engine for any more than 10 minutes, the noise returns when started again, until the engine is again warmed up.
My guess is this could either be a manifold gasket problem, or a problem with the tappets (if the Z20LET has them?). I can't specifically smell any exhaust gases in the engine bay, nor see any smoke.
Is the manifold easy to get to and check?
Is there anything I can do to check the tappets (if it has them)?
Does the Z20LET have an EGR valve? Had one of these go on my Vectra V6, although can't remember if it made the noise when warm?
My thoughts are that it can't be anything to do with the alternator or water pump as the noise disappears when warm. Am I right in thinking this?
Any help before I take it down to VX would be greatly appreciated.