I have the Akrapovic evo full exhaust in stainless on my E92 Msport, no drone but just like the others slight rattle at certain rpms. Solution: rattle usually comes from the rear center console slider. Open the slider put some velcro, fuzzy section where it latches. Gets rid of the rattle, I also added a clean microfiber towel folded up inside the tray to act as a sound absorber, no more rattle.
2011/335i Msport/ 6sp Manual/ K&N filter/ Akrapovic Evo Exhaust System/ FORGE FMIC/ Cobb Stage 1 + FMIC