So for about a month my 07 LSJ has had a slight tick when under hard acceleration during higher RPM's. then yesterday as i was accelerating my engine got considerable louder and there was a much louder rattling sound that only occurred when i hit the gas. there where no CEL codes thrown but i am pretty sure this is my cat that has went bad and i should see my dealer about the special coverage. what do you guys think?

i am also concerned as to what the dealer will say because there is no CEL and i have the GMPP exhaust with a flowmaster muffler. as i cant really afford the labour for them to pull it off.

Thanks