M30 engine with valve tapping noise. Perfect compression. Set valves. Checked rockers for cracks with small pry bar-none. Visually inspected upper head surface.
Pulled head to inspect valves and top of pistons for evidence of contact-none.
Reassembled. Noise still there. Thought it must be wrist pin or something near top from sound, but pulled head (Again) and disassembled head (which I should have done the first time)and found one rocker that had a soft spot on the cam rubbing surface that cam had made a slight concave depression into the rocker surface, but which had not dqamaged the cam (or even marked it) at bit.
New one on me!