Exhaust Noise, please help

Well, ive been driving around with a new exhaust, header back, and ive been noticing a raspy noise, sounds like metal against metal, like a vibration, thats the first thing i checked and it was nothing. I made sure of it. The place i had it installed at said that it was my "catalytic converter" even tho the "high flow" one i bought was pretty much just a resonator. So, they said that it was resonance in my exhaust system creating that noise, i figured they were right so i bought a new catalytic converter... same thing happens. It turns out to be a little quieter but its still definately there. It occurs under a little more throttle, from about 2000-3000RPM and then again at 4000-5200RPM its like its a resonant frequency er something, i cant seem to figure out what it is, ive heard of some people saying that it might be the piece of flex pipe in my car. Im positive its not my muffler though. The reason i think it might be the flex pipe is that when i bought the header off ebay (kinda stupid i know) it turned out to be one that wasnt an exact fit for my car but the place i installed it at said they would make a custom fit bracket so that it fits. (it hangs about an inch and a half lower where the bracket on the pipe mounts to the bottom of the engine block, also where the flex pipe is). Any help on this would be greatly appreciated.

Thanks alot guys

Sorry its a 1992 prelude SI if that helps at all

Do you have a new catback system?

it might be rattling against the heatshield

I have a new header, and cat back yes. I also checked for all the heat shield rattling, what bothers me is that if it was that, it would do it throughout the rpm range, not at certain points... still lost :uhoh: