I’m having trouble imagining the privacy concern. If someone’s vehicle is topping 90db then it’s hard to argue what they really want is privacy, and even the most invasive monitoring method I can think of (widespread mics) could be nerfed by requiring hardware that only responds at db threshholds well above conversation.

Probably more likely to get harassed in the country for it because the cops gotta fish harder for their extortion money/pay.

Ive been pulled over multiple times with brand new stock exhaust on a stock vehicle cruising at 55 because the body looked old and rusted and the cops were looking for any plausable excuse. With a real excuse they could throw tickets at you when they get frusterated with lack of other possible charges.