Well, I just installed a high flow h-pipe with cats and now it is making this hissing sound at WOT and under load. It kinda sounds like a fender CAI sucking in air. It is constant and doesn't have a pulsating sound like an exhaust leak. Could this be from the pipe leading to the smog pump? If so will this damage the the cats? Could this be normal? I've never heard this sound before. Thanks, any help appreciated.