As the cat sounds like it is probably screwed and therefore not doing it's job , my suggestion is to remove it and , err , eject the honeycomb stuff inside with a large screwdriver.
This will get rid of your noise.
Note to the EPA who are reading this , nismoman18 is only going to do this while at the racetrack.
For all other times , he will go and purchase a new Hiflo cat at a cost of about $300. Yea riiiight.
Ohh and btw , the reason the light probably went out is that there is nothing much left to overheat, hence the overheat light has gone off. Was there any mention from the guys behind about sparks and shit coming out the back ?
Cheers
Ken