This only started last week, but on occasion during the day we hear a "humming" noise coming from out electronics cabinet. (Unit was installed Dec 2014). It kind of sounds like your cell phone when on vibrate only, sitting on the counter. It only lasts for a few seconds. Sometimes it occurs once, https://100001.onl/ https://1921681254.mx/ https://happymod.site/ other times can be 2 or 3 times in a matter of seconds.
Yesterday, it occurred every 1-1/2 hours or so, today only twice all day.
The front panel doesn't have any lights on except The Online Indicator is green.
Any suggestions as to what we can do to troubleshoot this?
It could be the sound of the UPS's inverter kicking-in possibly to compensate for some out of range voltage or possibly the UPS doing a self test. Does the UPS have a network card and if so does the web interface show any errors?
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