Not condoning this activity but:
If you have an aftermarket exhaust and you get pulled over. Its probably because you were dicking around. My 2006 WRX is catless and pretty loud, see here:
An easy excuse if your exhaust is louder than a Camry would be that it is an SPT exhaust or something; a factory upgraded exhaust that is 50 states legal, and OEM. Even if something like this doesn't exist for your particular car, its still something that is well know to exist in the eyes of most people/cops.
Best way is to have a 100% legal car that has a valid sticker. Its your choice to be loud or not, when you want.