Sounds more like a diesel engine which has run out of lube oil than something electronic.
JimB
in fact, yes, now that i think of it, it really sounds like a diesel engine xD
what's it's "continuous load" rating? i think you'll find it's about half of what you think it is. sounds like you're looking at it's "peak load" or "transient load" rating. also remember that the power factor of your power supply might be very low, so the actual current drawn is so out of phase with the voltage that the actual VA is much higher than the "wattmeter" on the UPS is saying it is. this is a common problem with switchmode power supplies, is that their PF is somewhere between 0.3 and 0.5, because they present a primarily capacitive load to the line this tends to throw most "wattmeter" readings way off, because the "wattmeter" is assuming the voltage and current are in phase. cheap UPSs tend to have cheap "wattmeter" circuits, where better UPS designs will have a wattmeter that also measures PF and give a closer approximation of the true VA of the load.
to paraphrase Audioguru, you're probably reading a "WHATmeter"...
(f**, firefox died, and my reply got deleted before i submited it x.x)
summarizing, my supply has really good line regulation (below 3% for each voltage line), and the PF is always above 0.8 (active PFC). the LCD has a switchsupply inside but it's roughtly ~80W, so doing some heuristics, yes, i'm probably overloading it :-(, but still i'm not sure, i'm not even using the 60% of my supply capasity, and at 0.8, 700W would be 875VA....by 0.6 = 525VA. the lcd lets say 0.4 then 80W would be 200VA, then the modem and the router transformers are 4W, at 0.1(random, don't really know how much) would be 40VA x 2 = 80VA
525 + 200 + 80 = 805VA which is still below the 1200VA rating
even with the supply at 100% (whch is far from being real) everything would sum 1155VA, still below, at it's limit bstill below.
so then, any idea of could that sound be?, something is breaking or is it just an alarm, or just plain cheap ups that can't withstand what it says?