really wierd rattle

[Bfulgham]

driving slow on a rough road I get a rattle that sounds like it is coming from around the fire wall. Here is the wierd part , it only does it after driving at least 15 miles. You cant make it rattle untill you get it warmed up by driving. The dealer cant find it and I had the front end alighned and,no indication of anything that would cause a rattle was found. I am taking it back to the dealer but would sure appreciate some insight. I cant hear it from the outside of the truck.

Thanks: Bob

 

[rbattelle]

Sounds like something rubber or plastic vibrating against the firewall. When it's cold, the material is stiff so it stays put. When it's warmed up, it's more plyable, so it vibrates. Just a guess.