No experience with BDR or FFR side pipes, but I replaced the overly restrictive inserts in my pipes with Patriot auger type muffler inserts (
http://www.summitracing.com/int/part.../model/patriot).
When I first put them in I gave the blades a bit of a bend so they'd fit in the pipes, but they rattled like crazy and drove me nuts - especially when coasting. I pulled them out and re-bent the blades so they were a much tighter fit - tight enough to need a small hand sledge and a block of hardwood to drive them in. No more rattles.
