I bought my 2004 brand new. Love this truck. Just treated it and myself to some new Michelin tires today. It's at 170,000 miles. While enjoying that new tire ride and feel on the way home from the shop my wife mentioned that the muffler seems a little louder than normal. I can't disagree.
Question is, any replace a muffler and if so,did it drop the cabin noise?

 

Go look at it. Are there and holes or corrosion? Replace it with an OEM if you want quiet.

 

It might be a manifold leak??