Clicking noise in engine during idle

[Cecil-Indiana]

I bought adjustable lifters and new springs when I rebuilt it 3000 miles ago.
New development: just pulled the cam and all 16 lifters and the lifter on the exhaust valve on the 2nd cyl. On the drivers side has a divot worn in the cam surface on the lifter perhaps .030 deep and slightly off center. Cam lobe is marred but still mics same as other lobes. Going to the machine shop tomorrow with the cam and lifter to see if he can shed any light. The cam is a mild 3/4 from Isky.