I've got some hard-learned experience with loud exhausts...
The first time I got pulled over he gave me a lecture about it not being able to be any louder than stock... I politely informed him that the exception was that it remain under 95dB.
He disagreed, (i.e. told me I was full of it.) and then pointed at the hood scoop, wing, and gold rims with his pen, stating "I understand you kids like modifying cars, but it's too loud."
Clearly had no idea what he was talking about since everything he pointed to was OEM... I contested the ticket, showed up to court with the statute in hand, the police officer admitted that he
didn't know that was a law and I still got stuck with a fine, due to the last bit about having to prove it. When asked where I should go to prove it, nobody had any answers...
The second time, was becuase the first time was on my record and the cop was having a bad day... continued to write me a ticket with a smirk on his face as a fleet of Harleys drove by.
Other than that, I had been pulled over no less than 5 other times for my exhaust... when I
politely (I stress polite, ALWAYS be nice to police officers, they're typically pretty reasonable if you don't give them a reason not to be.) explain to them that there's a decible limit, they go double check and tell you to have a nice day.
Sorry for the long winded response, here's the statute... leave a copy printed off in your car if you're worried about it.
http://www.mainelegislature.org/legis/statutes/29-A/title29-Asec1912.html