lifter noise on VQ30 with GC

so i'm a little puzzled by the emergence of a lifter "tapping" sound on my 99 nissan VQ30. can anyone help me out here. 80k on motor. No previous lifter tapping. AutoRX at 76k. Running GC now with LC20. Had previously run Havoline 5-30 and ST syn 10-30. Initially, the GC seemed to quiet the motor down a bit (not that there was any pronounced tapping before, it just seemed to deaden the normal valvetrain noise). But 4k into the OCI it has developed a definite "tap" that does not go away when the engine heats up. I think it's the #1 cylinder on the back bank of the motor - so adjusting the valve clearance is a big job. possible it could be the timing chain - not sure what a noisy chain sounds like. what I'm hearing is an audible metallic "tap-tap-tap" that increases in speed with the engine speed and seems to be coming from inside the head near #1. it is not the light ticking from the fuel injectors on top. will this cause excessive wear if not fixed? what might have caused this? any suggestions? thanks.