Both TC and Rotorspeed are right to a degree, however there is no argument until some actual facts are put down on the table. Perceived noise is what it is all about. Once your ears are tuned for the noise there is no hope for the pro heli lobby !!! Mrs 500 can here me coming home long before anyone else can even hear the machine ( probably to make sure her other man has got out the house ! ) My grandparents lived in London with their back garden edging on to the main SW rail line they could never hear the trains yet used to keep me awake as a kid on visits !
Perhaps Tony could be more specific with actual details