Bmw M3 Competition 2025 Exhaust Valve Mod. From what i've read, it's meant to give that nice sports + sound on any setting (ie. The time now is 03:35 am.
All you do is put car in sport, visually make sure valve is open, then pull the fuse = permanently remain open. Imo easiest way is just pulling valve fuse in the trunk (f203).