hooper2

On decel my 97 lt1 makes an almost air-brake kind of sound from the exhaust around 2500-3000 or so rpms. I'm thinking it has something to do with the egr/air system.

Also, if I rev it at idle, I get an almost backfire up around 3.5k-4.5k rpms.

technical

Do you have a high idle? ...then check to see if the EGR is stuck open.
Otherwise maybe you blew a gasket near the mainfold.