there are some posts in this N55 section with sound clips of the exhaust.
See this one for example: http://www.f30post.com/forums/showthread.php?t=755754
F30 335i Msport Estoril Blue/Black leather sport auto. black grills, Performance Exhaust, HK,
On order: F30 328i Alpine white/Coral red Msport 6MT, HK, Zenons, msport brakes, black grills and black side sills. mperformance exhaust