For some reason starting the other day my muffler is making a really low tone and like sounds like a cheap exhaust when I rev it. It's coming from the back side (side facing the engine) of the muffler. What would be the problem, a broken gasket maybe?

 

is it a stock muffler/exhaust?

 

Stock muffler

 

exhaust leak? That happened to me and thast what actually prompted my welding of my aftermaket muffler on waaaay back when. If its stock exhaust it's probably corroded, take a look under, have somebody rev oyur car too so you can hear where it's coming out.