Golf 1.9 TDI tapping noise

[gkm24]

I have a 58 plate 1.9 TDI Golf 58k miles ( its a 110Hp blue motion)estate manual which started tapping. I have replaced the camshaft and hydraulic tappets which all sound fine at idle but at about 2500rpm it sounds as if the tappets are really noisy.
I am very familiar with these engines and worked on them for years but never had this problem. I'm thinking that it may be something other than tappets but have never heard this on a PD engine before.
Anyone had any similar issues?
Thanks for any help.

[Crasher]

Could you PM me the cars reg?

[Crasher]

There is a known problem with the boost control valve that can cause rattling noises to be transmitted through the bulkhead, if you dismount the valve and then try it the noise may go and then there is an updated pipe 03G 129 808 C which solves the problem but you noise gives the impression of being too sharp for that and a similar problem can come from the EGR valve where a restrictor valve has to be added to the feed line, 03G 131 050. Without hearing the noise first hand it is all I can think of. What make of cam and lifters did you fit with the part numbers if possible? Did you rest the injector lever clearances?