Make your BMW M4 sound burly with an Akrapovic exhaust. Take a listen to how it would sound in this video. I don't think that you'll be disappointed.
Guys at European Auto Source put an Akrapovic Evolution Titanium exhaust system on an M4 with some Evolutino Racewerks Competition catless downpipes. It not only gives a fuller sound, it also boosts HP and torque.