http://www.bobsmuffler.com/noise.htm
It's pretty straight forward to be honest, have mufflers, don't be obnoxiously loud. If you're above 95db, you are a douche plain and simple. Test pipes/catless and stock exhaust has always been the best medium for power/sound and being stealth since it appears stock.
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2006 Z4 M Roadster Black/Imola Red, FBO VF-Engineering, e85 Flex Fuel-Sold
2012 BMW 135i N55 DCT Alpine White/Coral Red, FBO, TBI, Full e85, JB4 BEF-Sold
2006 Z4 M Roadster Black/Black-Sold
2021 M2 Competition DCT Hockenheim Silver