Everything is stock, the only mods i have in the car is the Performance Friction brake pads hence you hear the crazy brake squeal sound.
After taking the car to track i realized the exhaust sounds much better afterward. I guess it expands due to constant high temperature exhaust coming out and resulting in a stronger sound.
if you go to the youtube channel of that video, you can find periods of cold start and idling while waiting in the line.
BMW M3 E92 - Silverstone II