I heard a rattle in my flowmaster muffler and thought i was gonna have to buy another one.. then i got a magnaflow catted X pipe and the sound was gone ever since
wierdest thing.. but if you haven't changed midpipes yet, that may help
I've ran Dynomax mufflers in the past and never had any trouble with them. I had the welded ones with the heavy cases ... they weren't real loud, but had a good sound to them.