I did a muffler delete on mine and basically did an axle back straight pipe and also added a M5 M Performance style diffuser.
Another forum member did the same while keeping the stock diffuser (later switched to M Performance diffuser):
https://g30.bimmerpost.com/forums/sh....php?t=1429679
You can also get something from AC Schnitzer, Armytrix, Remus etc if you want to be able to control the sound level. Most aftermarket exhausts for G30 has quad exhaust.