Here's the deal.

I have an older cattman Jet Hot y-pipe. The pipe itself is in good condition. The pipe hisses at WOT, but that is normal...

My pipe hisses EVEN louder than at WOT when I have the RPM's above 3k and I take my foot OFF the gas ( ie. Shifting ).

I would assume that I have a leak somewhere....but wouldn't that make the hissing noise all the time?

Is this hissing normal? I don't remember hearing about this.

I put in an RT cat a few weeks ago, but it had been doing this since I got the y-pipe installed, so I don't think the cat ( or those wonderful flanges ) are the problem.

Thanks.