I've got a '99 Silverado 5.3, 4x4, ExtCab, SB with 130k on it. I installed a Gibson Catback 100k ago. I am getting a weird rattle out the exhaust, but everything looks good on the outside. I pulled it loose after the cats and no rattle. (Just real loud) Could the muffler be coming apart inside? One other thing. Is there supposed to be a gasket or something between the cat pipe and the rest of the exhaust?

Thanks

It could be the cat.