hi.. I have an acer 23" LCD monitor. When the computer switches to UPS power, (for eg if I turn of the power from the wall socket) i hear a moderately soft buzzing noise comming from the monitor. What could the cause of this noise be?
The noise is there even when the monitor is in standby mode.
(I'm running the screen at very low brightness and contrast if it's relevant.)
The buzzing normally changes if you change brightness/contrast. It should reduce buzz if brightness is turned up.
I'll make an informed guess here.
I think it's coincidence - you're running on low brightness so there's a buzz.
But I can't ignore the UPS point. I'd bet that the UPS (maybe a cheaper one?), without proper mains synchronisation (50Hz in the UK, 60Hz in N. America) the UPS A/C output is not perfectly sinusoidal which can induce the buzz via the input mains component. I would expect the buzz to disappear if you turn up the power demand via the brightness control, but that depends on the monitor's design.
No it won't damage anything if my diagnosis is correct - i.e. on battery driven UPS only. It means that the sinusoidal interference or drift is causing an electrical resonance that comes out in a buzz.
Outside chance it'll go away if you separate mains and video cable - no overlay. I've seen that before on CRT monitors.
And you can confirm that it goes away when your UPS is mains connected? Yes? If not then you do need to contact your seller because something would be wrong.