Man oh man, im running out of guesses. When my rockers where hitting my oil baffle, the noise radiated through the whole upper intake so it was a simple, but troublesome time figuring it out. Only thing else i could think of would be detonation. But even if its that, theres so many things that could cause it. If you had nitrious or a blower, inadequate fuel can cause detonation as well as too much timing. Too hot of a plug and not high enough octane gas or bad gas also can cause detonation. And opposite, bad gas with too much timing. Keep us informed on what you find when you break it down, im interested on what it could be.