I looked into this myself. Legally, there is a set decibel range and a laundry list of specification which must be met for an officer to legally measure it. So, right out of the gates, it's BS. It would be like saying that he's giving me a speeding ticket because he -felt- I was going too fast. There are set parameters for noise as there are for speeding. He thought my exhaust sounded too loud? There's no law for changing your muffler as long as it passes emissions and doesn't exceed the decibel level threshhold. There's no possible way this legally holds water.
To answer a few questions:
-it's the Invidia N1 Race....so yes, it CAN be loud...(if I drove around in 2nd gear...which I don't) or if I didn't shift until 4-5k. However, driving around normally, it's sounds a little throatier (a change in pitch but no louder). I was driving very calmly...shifting around 3.5k.
-I never go down through Phoenixville...maybe a couple times a year.
-I was driving very calmly in the midst of traffic. There was a line of cars in front of me and behind me.
-I do have tinted window: 35% and in PA, legally, they need to be 70%. You can easily see into the car. They obviously look tinted, but not dark enough to cause a problem. However, he never mentioned the windows. At least that would have been a valid citation.
If they want to do the decibel test, I'm, very confident I would still pass without any problems. They measure your decibel level at a certain height, from a certain distance. There are two groups of measurements referring to the composition of the driving surface (e.g. a paved road is a hard site) The "soft site" parameters: 76dbs under 35mph, 82dbs over 35mph...and "hard site" parameters: 78dbs under 35mph, 84dbs over 35mph. I can drive by in 6th gear (since RPM is not a parameter for testing) and it'll be as quiet or quieter than every other car on the road. So even if they want to test me after the fact, I wouldn't worry whatsoever about passing.