95 cav backfire 2.2L

my 95 cavalier 2.2L started to backfire out of no where. i replaced the spark plugs and it got a little bit better. but it still backfires and now it sounds like i have a performance exhaust even though the exhaust system is completely stock. when it first started backfiring, it was inside the engine and through the exhaust. now that the spark plugs are replaced, it only backfires inside the engine which leads me to believe that my cat is clogged. im going to replace the spark plug wires today and see if that doesnt fix the problem. does anyone have any thoughts? :banghead: :shakehead

Personally I would check your header and exhaust to see if it's got a crack in it. If there's a crack in your header it would explain your engine sounding considerably louder and it would also explain why the noise is coming from inside the engine compartment.

Or it sounds almost like the flex pipe right behind the headers has a hole in it which would make it sounds incrediably loud and might also cause some of the back firing just a suggestion.