a small exhaust leak can sound like a mechanical tick, but it usually only happens under load. On my old 360, I did have a little valvetrain noise, nothing loud enough to be annoying, but you could hear it a little with the hood up. the rockers were tight on the shaft, no real noticable wear (egg shaped holes in the rocker, out of round shafts), but the rockers did have some freedom to slide sideways on the shaft, and I'm confident that was the sound I was hearing. some shims or light springs between the rockers, and the rockers and hold downs probably would have eliminated the noise.

setup was a comp XE262, stock pushrods, rockers, and shafts.