Hey, before you get too crazy, make sure your header pipe isn't loose up at the cylinder head. I just had a 2003 Speedmaster come in for valve adjustment, customer complaining about loud scary noise coming from head that just came from out of nowhere. One of his stud nuts was missing and the other was backed way off. The pipe must have just finally backed out of the exhaust seal because it was extremely loud. I replaced both nuts and lock washers and had a happy rider drive away owing me a coffee.
