Sounds like it has a fan inside to cool it, and the fan is broken or off-

I have several inverters, all with noisy fans or annoying low-voltage alarms

It does not have that annoying fan sound that the cheaper models do

Sounds like it has a fan inside to cool it, and the fan is broken or off-

Fan makes a small noise simply because it has a

Great little device and works as it says under product information!