Hi there,- have a stand alone off grid EasySolar 1600/12.
It has PV and batterys,- they charge fine and are full.
There is NO connection to the mains grid.
There is a buzz / hum from the inverter [torodial transformer] which was not there when new.
The inverter works fine and produces power,- very nicely.
This hum is there even when the mains power output connector is unplugged from the bottom of the inverter [so not even wiring or socket connected!]
the hum is NOT the cooling fan,---this is stationary normally but does kick in under load.
The inverter did not make this noise when first fitted.
I would appreciate any advice but I feel that this unit should be returned to victron