So I put the stock muffler back on as the SuperTrapp was just too noisy for the neighborhood and now there's an annoying rattle / buzz inside either the header pipe or stock muffler.  Sounds like a loose baffle maybe.  I checked there's no metal-to-metal contact against the frame or heat shield outside.  Any similar experiences or ideas?  Maybe all those backfires just blew the double-wall loose inside the header  

Did you try the fiberglass in the supertrapp?
I haven't cause I'm happy with just disks.
in my neighborhood, HD's roll by trying to keep their wake the dead bikes down to a roar.

OK, problem solve-ed, as Inspector Clouseau would say.  I couldn't stand the annoying rattle that resonated at certain rpm's so tore the OEM muffler off again.  Turns out my wild hunch the exhaust header inner tube was loose proved correct.  How, you say?  The inner tube is located at the muffler end by a split sleeve spacer.  When I first installed the SuperTrapp I had to cut 3/4 inches off the spacer through a spot weld to slide it up far enough so the mounting bolt holes lined up.  Now back to the OEM muffler and the shortened spacer vibrated loose causing all the rattle.   Just have to cut back to 6 discs in the Trapp to keep the neighbors calm.