Chevrolet Repair: rattling noise under truck, chevy tahoe, cat converter

Question
ever since i added premium gas in my 1999 chevy tahoe, my muffler has been making a rattling noise. i looked under the truck and nothing is loose. What could be wrong with my muffler and how can i fix it?

Answer
first be sure it is your muffler rattling and not the cat.converter. odds are i think you will find it is the cat rattling and will need to replace it or have it hollowed out. if it is the muffler its just the baffles inside and you would here a noise difference as it gets louder. just reach under the truck and hit the cat. if that is what the noise is you'll hear it when you hit it.
hope this helps.