I wouldn't worry about this at all. When I first moved to Maine back in 2003, I had an 01 2.5RS that had a loud exhaust. It wouldn't pass inspection because it was too loud, and the law back then stated that your car couldn't legally be louder than stock. So I asked the dealership (Patriot) who failed my inspection to provide proof that it was excessively loud. I mean, you could hear it, but they didn't have measuring equipment to actually record the decibel rating of the exhaust. So I called the Maine State Police (hereafter referred to as MSP) and asked them about it. I spent a ton of time on the phone with them, and basically this is what transpired:
MSP: Your car has to be within acceptable stock limits for noise output.
me: what's acceptable?
MSP: Anything under 95 decibels.
me: how do you measure that?
MSP: with a decibel monitor.
me: is that part of a normal inspection process?
MSP: no.
me: where do I get my exhaust decibel measured?
MSP: I have no idea.
me: does the state have official test equipment?
MSP: No.
me: how can you possibly hope to enforce this law?
MSP: we can't. the burden of proof is on the owner of the vehicle. If the garage feels its too loud to pass inspection, the owner must replace it, or find a garage that can measure sound output. You'll probably have to go out of state for that.
me: Okay, so assume I find a garage to measure it, is there some sort of official form I have to get filled out?
MSP: no.
me: so how do I prove that I've had the volume measured?
MSP: get a receipt.
me: seriously? that makes no sense.
MSP: it's your responsibility, sir.
Being young and foolish and too broke to buy a new exhaust, I actually called everyone under the sun, including the exhaust manufacturer looking for a way to fix this problem. In the end, I just took it to another shop, who inspected it without saying boo about the exhaust level. By the next year, I had a quieter (but still considerably louder than stock) Greddy exhaust on the car. I took it back to Patriot. They passed the car without mentioning the exhaust.
So the moral of the story is...this law is unenforcible and worthless. If you get hassled somewhere because your car is too loud, just go somewhere else. Or buy a baffle to put in the tailpipe when you go for the inspection...