2.5tdi tapping

My a4 2.5 tdi 180 seems to have developed a tapping noise coming from the top end It only does this when cold on startup its noisy at first untill the oil reaches the hydraulic lifters for 2-3 seconds then there is still this faint tap which stays untill the engine is fully warm. The car purs lovely when warm with no noise, there is plenty of power with no smoke and i cannot fault the drive. I have tried all the cheap remedies like oil change engine flush etc to no avail

The noise is coming from the right hand bank. I religiously change the oil every 6k with proper vag spec fully synthetic oil and i have looked down the filler tube with a torch and the cams look spotless on the two lobes i can see.

Does this sound like i am going to need a full top end rebuild as i hear horror stories about the chocolate cams fitted in these engines. It's a 2001 AKE with 134k so right in the ball park for this problem

Have any of you guys had simular issues?? or could it be something more simple??

Cheers

Where are the oil retention valves on this engine? i was not aware there was any?. I thought it only had the usual hydraulic lifters with rocker arms/pads ??

If these valves were at fault wouldn't the car be fine once it had been running for 5 min or so?? surely once the engine was running it would refill with oil and all would be ok?, Maybe im missing something, The tapping seems to be worse at cold but once the engine is nice and warm say 20 min drive the tap can barely be heared atall. i would hate to take it to a garage for them to tell me all the valvetrain needs replacing.
Would these valves cure the tapping once the engine had been running for a few mins?

Thanks for the replies chaps.

Anyone?

Just thought i would share my update

So off come the cam covers i look down expecting to see the usual cam wear with eaten follower arms but no. I am very suprised to see there are roller rockers looking at me!!, At a guess i would say this is a later engine perhaps fitted before i bought the car a few years ago ?? the cam's look clean with no obvious wear apart from what looks like best described as brown residue in some of the chrome on the lobes ?? although not at the lobe "tip" but just before it on some of them. the cylinder heads are very clean with no carbon buildup usually found in engines with low oil changes so my best bet now is possibly a noisy hydraulic lifter perhaps.