If you see the folks in the next campsite head inside their RV everytime you fire up your generator, then you know it's too loud. I'm sure there's something on the books about the maximum allowable decibel level, the regulations I've seen have to do with hours of operation, usually 8am to 10pm. The rule of thumb most RV'ers use is: If my generator is running at full speed would the noise bother me if I was sitting in the campsite reading a book. Can I carry on a conversation without the need to talk louder than normal. Look for the generators that indicate super quiet models. Hondas seem to be the generator of choice as long as they are the fully enclosed models like the 1000, 2000 or 3000ei. When you get into the 5500 and above range then you want to look at Onan models. I run two Honda 2000 sets connected with a parallel kit when I need to run the A/C or washer/dryer. At full throttle you can barely hear them 20 feet away. At one time I had a Honda 6500 contractor model generator and everytime I fired it up you would see folks for several campsites in any direction get up and go inside their RV's. I sold it and got the two 2000 models.

FYI---and you may already know this but here are a few decibel levels so you can relate them with the actual sound level of the rating.   20 dB is an empty theater,
60 dB is normal speech, 100 dB is heavy manufacturing, 130 dB is pain threshold.   
 
Flyone