Lo and behold I have an exhaust horn. Single orifice steel. The operating mechanism is stuck. Is there an easy way to unstick it or do I have to take it off and take it apart?
Try using a torch to heat it. Let it cool, apply penetrating oil. Try to move it. Repeat until it moves.
The best penetrating solvent I have found for exhaust systems is "Mopar manifold heat control solvent", it used to be sold at any Chrysler, Dodge, or Plymouth dealer. I don't know if you can still get it today. It has worked for me when nothing else would.