I took my 2005 V6 Automatic in for 33K mile service. I had been noticing a vibration coming from around the muffler area, especially when cold or when revving the engine. The dealer advised my muffler was bad and is ordering a new one. I have seen a lot of dialogue on replacing the stock muffler but has anyone else had a factory one go bad?

Also, is there anything I should be watching for as I approach the end of the factory 36K mile warranty?

The only problems to date are:
--Replaced the Shaker 500
--Bad fuel sensor switch
--Battery went dead

Other than that I just have had the usual gas fill up issues -- I just turn the nozzle 90 degrees.
Thanks.