This is my UPS.
When power goes out and the ups kicks in, the single wire that originates from the UPS to all the fans/savers etc emits a buzzing noise. And naturally the noise is at it's peak in the sockets area(ups powered sockets for charging mobile phones etc). It is a very audible constant buzz type of sound. It doesn't mess with anything seemingly, but I was wondering the reason behind it.
Could it be because the UPS is modified sine wave? Or the wiring is single wire 'thin'? Or maybe something else.
Any help would be appreciated.