As the others said it's most likely reversion, caused by camshafts that actually have overlap(intake and exhaust open at the same time). Scares the crap out alot of folks when they hear it after having an open air filter the first time.
Put the stock air cleaner on it long enough to check, I'll bet the noise goes away.
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2011 Merlot RGU, 103", SE204 cams, V&H Dresser Duals, Ness BS, Power Vision, Progressive 940s/Monotubes, 13" MadStad.
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