Yamaha, Power Source and Champion all make generators that generate less than 70 decibels of sound while operating. While proper craftsmanship and sound dampening helps to lessen the noise from a generator, any generator with an internal combustion engine is loud to some degree.
One of Yamaha's quietest generators is also one of its lowest powered, generating 2,000 watts at a 51.5-decibel rating. Power Source's IG800W portable generator only puts out 800 watts of power with a 56-decibel rating. Champion builds a generator that outputs 1,500 watts of power, but the noise rating is 65 decibels. While all of these generators produce a low amount of power, they are quieter than others, which can get as high as 70 or more decibels. Solar-powered generators don't have an internal combustion engine or any moving parts, and thus generate no noise at all.