I recently had my WSP SS y pipe installed, and when I go over bumps, it sounded like the Stillen exhaust tip was banging against something, which didn't happen before the install. The guy who installed it said my old y pipe's flex section was totally gone. So now when I'm in a parking garage and can hear the exhaust real well, I think I can hear the "bees in a can". I thought the WSP pipes werent supposed to do that? But now I'm thinking that since the y pipe was bad, the cat might also be bad. I read about 007's cat having the honeycomb thing dislodged, and I'm thinking this might be my problem. It sounds like something is rattling around in there, which I didn't hear before the y pipe install. I'm thinking about just getting a Carsound cat, but then I read on Custommaxima.com that cats for 95/96 and 97-99 are different. Since I'm planing on selling my 95 GLE for a 97 SE, I was thinking about holding off on the cat until I get the new car. I also read on here that the exhaust length is slightly different for 95/95 and 97-99. I want to swap my whole exhaust (y pipe, b pipe and muffler, and maybe cat) from mine now to the new one without a problem.

Also, my gas mileage has been real low the past couple months, about 16 MPG in the city, but I have no lights on, and I have new oil and a tuneup, including new filters.

Since this post is so long, I'll re post my questions....
1. What is the noise?
2. What is banging around my muffler?
3. Are cats the same for 95/96 and 97-99?
4. Are the exhaust lengths the same? (I'll guess and say yes)
5. Could the cat be a source of my low MPG? (Yes again?)]
6. Why else is my MPG so low?

Sorry about the newbie-esk questions, but I was expecting a loud, but not annoying sounding exhaust. And I searched for "exhaust length", but only came up with race stories