You dont have a leak. The hiss/rattle/metalic flutter on these cars once you go test pipes + exhaust is, IMO, horrible. The LTH's are amazingly gorgeous pieces. The fact they're being made by F.I. is an honor as their work is proven perfection. Only problem I see with them is they magnify that test pipe rasp 2x. Maybe they made a way to make the rasp sound good, ie; rattlesnake
My opinion on the rasp is, its harmonic. It seems when you hear it from below the car you can nearly feel the rattle coming from right before the Y/H/X setup. Seems that exhausts that have resonators right before that point in the system have MUCH less rasp than anyone else. Also, and I'm not sure how true it is but I heard "true duals" that have no connection to each other have no hiss, but I cannot confirm this.
Tony - After all the exhaust issues i've gone threw etc etc I may cave in and order a system from you after the SC install. Most likely 18"/CF - I really love the sound your system gives out. Good work, top notch!