So a while back I noticed there was a somewhat small hole in my muffler. I have been very careful when going over bumps and stuff so I am very sure I didn't bottom out my car. Also the hole looks as if it has been shot from the inside out. Shortly before I noticed this hole I was on the highway and heard what sounded like a loud ping or crack coming from the underside of my car. So I am not sure what happened. I have no idea why this hole is there and it seems to be getting much larger too. The baffles and stuff inside my muffler were all loose and rattling long before this happened also. So... Back on topic, my friend suggested that possibly my cat is totally dead and making bad things happen in my exhaust? It sounds dumb, but it is possible? (bad things being corrosion or something) I did some research and it said if your cat is bad that you get awful gas milage and other such problems that I have noticed happening in my car. For the gas milage I wasn't sure if my O2 sensor was bad or what... My car also has been getting pretty stinky if that makes any difference? Sorry there is so much to read but can anyone help me out on what the problem could be?

 

Anyone? Is the sensor bad? Is my cat messed?