Quote Originally Posted by evillecutter View Post
is this mythical warm up valve supposed to be inside of the muffler or exhaust pipe? my muffler has a rattle when i rev up the engine and im going to get a new one (non oem) - if noone knows ill save my old exhaust and get to it sawzall style then let you know what i find
I just asked Jerry again. He said inside the muffler. And, for sure, the 98 and up Troopers had this "feature". It was supposed to help hold heat in the exhaust and help warm up the cats faster.

Kinda makes it sound like the same kind of thing as the Dynomax VT muffler -- expect the reasons for the valve are different (warm-up vs sound control).