i have a similar noise on the down throttle around 2000 - 2500 rpms
everyone i know tells me its normal with test pipes
it sounds like metal scraping or something along those lines its real faint but it annoys the hell out of me

 

I think i should record a video of my car doing it also, it is annoying but I somehow got used to it.. lol

XYZ looks very good.. i wonder how much it is gonna cost to have it shipped to New Zealand, or maybe i'll just get my local exhaust guys to build one with similar design..

 

I have Fast Intentions hfc's on my hr, hisses between 2-3k. The car has a little power loss there toowhich makes me feel it is indeed a leak in the y-pipe flex,, but afterward it's eyebrowraising torque-y fun. I personally think the hiss sounds kinda cool, yet mine sounds identical to a blow off valve, and I hear no metal scraping.

 

tell ppl it's a turbo? haha I told someone who drove my car it was all n/a, and ten minutes later he asked "is this super or turbo charged?" He's a smart kid too, so just have fun with the power and sounds=) Unless your exhaust falls off. Then get it checked.

 

lol im relieved to have found this thread. i have the same exact problem and its just like you guys described. hissing at 2K RPM when letting off gas. im just telling eveyrone who asks about it that it is a pressure release valve...story works every time..lol

http://www.youtube.com/watch?v=XKEkt...er_profilepage