Haha yeah i've heard a few guys have had this same problem. I've had my stock exhaust on since i got the EPA test, but i'm thinking about adding another muffer into the system, before the cat if i do decide to put it back on. Hopefully that will eliminate the noise!! Otherwise i'm helpless, pack it up, sell it and leave the stock system on. Or buy a good reputable Jap brand like a Kakimoto, trust, a'pexi or blitz system. I did heaps of research and i was soo close to getting one of these but in the end decided to go to the local exhaust place!! Ah well what can you do!