[Jgordon]

B&B had some issues with earlier mufflers with cracking, both internally and externally. You can see the extra bracing they welded on later models. Chances are that an internal baffle broke loose and is lightly vibrating against the muffler wall in that rpm range (typically a harsh point in the B&B range). I'm actually surprised you liked the sound prior to this, I had a system and couldn't take it, as has been the experience of a number of people on the board.

It depends on your preferred level of involvement as to how you fix it. You could try pressure at different points on the muffler body, and drill/tap a screw at the point where you find the best improvement from touching. Seems like a scattershot approach though. You could also ask B&B for a schematic of the muffler, and for their advice on how to go about it. At the least, you'd know the layout of the internals and could gauge where the break likely occurred.