96 Integra LS, had a flowmaster delta flow and some 2 1/2" piping welded on from the cat back out to the tip. On occasion (mostly when the car is not warmed up, but sometimes after it has) it will go from its nice deep tone to a high pitched LOUD LOUD LOUD rattling noise, sounds almost like there is a loose baffle inside the muffler (but the muffler was brand new). After extended highway driving, it usually wont do it for a while. I dont like my car sounding like shit, and can feel a power loss while the buzzing is going down. Is it just a defective muffler, or could something else be causing my problems.