Okay, here what I got:
Cattman Y pipe
Warpspeed Cat
Stillen B
Stock OEM 4th gen Muffler.
(Used to have the Stillen muffler on, but I was getting a little anoyed with the droning, so I switched back to the stock muffler.)
Now I have a leak, (It sounds awful.)
I pinpointed it for the most part where the Stillen B pipe fits together, so I sorta clamped it with one of those steel screw rings, you know the kind you use a flathead screwdriver to tighten/loosen.
After I clamped that tighter, the leak went away for a while, but now it's back, just not as much. (less noise)
My question is, does having the 2.5" piping all the way until the stock muffler which is like 2.25" cause the exhaust to find other exits along the way? Like not enough of an escape route and it goes and leaks out of the B pipe?

 

No.

Get better gaskets, tighten up your connections, etc.