Ok, so I jus had my FI HFCs installed this weekend and I'm starting to notice a loud fluttering noise coming from my exhaust on the deceleration (between 3-2 rpms). It actually sounds like there's a leak somewhere, but when on the lift...no one can detect a leak anywhere. It does not do it at all while accelerating, or when the system is cold. Only on decel, when system is hot. If anyone is familiar with Borla exhaust, there's actually a pipe connecting the two main pipes coming from each of the cats. The noise appears to be coming from that area. Mind you, the exhaust was on sounding fine with no noise with the stock cats. Can more airflow with the HFCs be the cause of this noise? Do u think it can resolved if I just cut that connection out all together so that there's no joining of the 2 pipes? I'm completely lost with this. I don't want to waste money to have exhaust all chopped up trying to get rid of a sound, while creating more unwanted ones.

 

HFC and Test pipes have been known to cause a "whooshing" sound of air on deceleration.

A leak should be detectable at acceleration and decel.

 

definetely from the HFC's, I had the same problem with my test pipes. eventually got on my nerves and put cats back on.