Have you tried to tap on the exhaust while the pipes are cold to see if you can get a rattle anywhere?
It shouldnt be too hard to spot from under the truck. I a good muffler shop would also be able to tell you.
My stock diesel exhaust rattles, only because I put a dent in the muffler the size of a grapefruit. Have you checked for any dents in it or places where it's been hit?
I haven't had this problem with my Dodge but my Ranger has some sort of heat sheild on that has collected rocks a time or two. You may want to check for that.
A forum community dedicated to off-road vehicle owners and enthusiasts. Come join the discussion about trail reports, builds, performance, modifications, classifieds, troubleshooting, drivetrain, and more!