I have a 2002 Xl with a 4.2 liter and 27000 kms on it, I had to bring it in a month ago for them to do the rear seal on the engine then the exhaust started vibrating, thought it was a heat shield or something. Well I brought it to the dealer today and guess what they had to order a new muffler for me, can you imagine!

 

them factory mufflers allways rattle...

 

It isn't a normal rattle you can here from a mile away I guess a weld let go inside or something

 

It shouldn't I have 38,000 miles on mine with no rattle at all...