Does the tapping frequency vary with rpm's? How about intensity/loudness?
A trick for locating the source of an engine noise is to take a long screwdriver (or other metal shaft) and place one end against an engine part then "listen" at the other end, like a stethoscope. If you find the source of the ticking, you'll know it.
Obviously, be VARY careful around any moving parts, belts, etc. If you are not familiar/experienced working on engines, best to skip this test for your personal safety.
Ha! I just looked at the engine compartment. Good luck finding exposed metal without removing that cover! Times have changed...