I've finally gotten to the point where I can't stand the under hood exhaust sounds of my '85 4Runner. It is either the induction noise from the FIPK, the headers (older 16gauge LC Engineerings) or the free flow cat.
The sound reminds me of when the old cat plugged up before I had the new motor. I didn't want to replace it since a new motor and exhaust was coming so I beat out the guts with a bar. It sounded like I had used beer cans for the exhaust and that is what this set up sounds like now.
I'm thinking about using some header wrap on the cat to see if that is where the noise is coming from. I put some wrap on the upper end of my headers a few months ago and it had no effect on the noise. Add to that some recent surfing on the net recommending against using header wrap on a daily driver's headers and I am going to pull the header wrap anyway. If the wrap on the cat kills the noise, I may very well go with leaving the wrap on and letting it possibly kill it and buy a different type next time.
As Popeye would say, "I've had all I can stands, I can't stands no more!"