FMF is pretty quiet. CT's supertrapp exhaust with disc is pretty quiet as well. Really most of the disc system exhaust's are pretty quiet outside of a few here and there like Sparks, Yoshi, etc.
and i beleive on the ct you can pull one disc out at a time until you get the desired power to sound ratio. Like if sound dont matter no discs and if it does all or some of the discs.