[Sharps40]

Whether or not its shaft type rocker arms or hydrolic lifter with the stamped rocker arms....

22 Million dollars (which I ain't got, but if I did I'd lay it on the dash) says its a rocker arm tapping or if hydraulic system, a lifter induced tap....betcha at higher rpm its either hidden in the general woosh of noise or oil pressure is higher/parts under load and the noise don't exist anymore.....

Do a hot engine valve adjustment, regardless of the type of lifter/rocker. In any event, if its a rocker, often the simple pressure of a finger on the offending rocker will eliminate the tap of the valve seating a bit too quick/hard and you know....it needs snugged down or lifter replaced, etc, etc.

Could be as simple as worn out rocker shaft or rocker studs, etc....specially if valve train parts like shafts, studs, nuts/balls/keepers was reused.