It is quiet, because the fan motor sits up in the attic rather than on the ceiling of the room, so most of the sound stays out of the living space. There is no official sones rating for it, since the noise depends on how it is installed, things like the type and length of the duct and how far the motor sits from the intake. As a rule, venting with the motor mounted away in the attic is quieter than a fan mounted right in the room.