Scenic engine tapping

My engine seems to be tapping. I've took it to an engine specialist who says its not crank or cam related. Originally thought it was tappets but these are solid and not hydraulic and very rarely wear. Took cam cover off and measured valve clearances they seem to be within spec. The engine builder suggested that its a timing issue maybe a tooth out. The only other symptoms are low power at higher speeds along with this annoying tapping. It sounds like a tappet. Has anyone else had this with an engine a timing tooth out? The car drives fine otherwise.