Originally Posted by JSLRedYJ
Very good question, mine does it too!
I'll be watching for an answer
Ha, ha, ha!
It would seem that ALL of us with Flowmasters and high flow cats have asked ourselves the same question!
This is just a guess, but I think that our Jeeps have always made that noise when letting off of the gas while in gear. IMO The difference being stock cat and muffler were restrictive enough to dampen the noise.
Remember how heavy your stock muffler was compared to the Flowmaster? Alot of engineering time and $$$ goes into designing a quiet muffler that has reasonable flow characteristics.