What engine??
Are you measuring clearances when engine is hot or cold?
Are you reliably measuring from the base circle of the cam? (ie double checking measurements)
Is it all of the "tappets"/"followers" making the noise or just one or two?
Which oil are you using?
How old is the oil?
What valve springs are you using?
Are you getting plenty of oil onto the cam and the "tappets"
What condition are the "tappets" in?
Are you using oil additives?
My experiences with cams approaching, and over 0.5" lift, is that there is inevitably increased "tappets" noise (but depending on profile). Simply everything is working harder (and wear out faster) because of the increased lift.