The noise sensors are so sensitive that you could get busted in a light aircraft, even with a windmilling prop coming in to land...For example Long Beach, if you shoot the ILS 30 late at night, then chances are you'll receive a letter from the Long Beach city (as has happened to many of my friends ) - trace you via Socal, regestration and hence pilot. After a couple of warnings you start getting fined.
Best way is to know where the noise sensors are and avoid them, and in the case of LGB, using the VOR approach instead and you will be safe.
Cheers
EA