okay, just played around a bit more and the sound is definately more prominent in the flex joints, but I agree with Tony that it is not the flex pipe themselves... its simply where the sound most easily escapes due to the construction.
I hear the sound generating in the cat and in the pipe directly below the cat, and this hiss/rattle then eminates most from the flex pipes in the Y. again, the sound doesn't make it to the muffler because I stick my ear right next to the tips of the exhaust and it is just the nice, deep "normal" exhaust without the hiss.
so I wonder, what would happen if a second set of resonators were added (in place of the flex joints). just a thought. I'm not going down that path personally, just ponerding.
Fast Intentions had great results with only their catback (on stock cats). Impressive dynos, and a BEAUTIFUL sound from the video. I am STRONGLY considering reinstalling the OEM cats and just enjoying the sound of the F.I. catback exhaust.