VAREX make adjustable sound exhaust, however it's illegal. I believe the HSV's came with this feature, the loudest was 90dB and low was X. However, you can set loud to be 108dB and low to be 80dB. Cops don't like you being able to adjust the tone when their not around etc. My cousin had it and it was pretty awesome. They're about $2k to fit and install last time I checked.