today i installed nismo catback exhaust + kinetix test pipes with the in-line resonator... i noticed that when i rev it up about 3.5~4 K and release the throutle there is a hissing sound comes like a (PISSSSSss) or (hiissssss) i know its not a BOV j/k (no turbo yet)

so any what have any idea about this one ?? is the sound normal or there maybe some leaking somewhere?

 

sounds like exhaust leak?

 

yeah might be exhaust leak, you should get your installers to check it out.