This is a unit from when APC and IBM were all chummy and made UPSs together.
So I got this thing refurbished from excess UPS. About a month and a half after I got it, it would start making this buzzing noise every once in a while for maybe 15 seconds at a time. It rarely happened during the day, but at night it would happen as often as once a minute for long periods of time. Occasionally this caused the buzz to come out on the end of my speakers.
Obviously, I didnt like this buzzing very much. I told excess UPS about this and they replaced it. This didnt fix the issue. It has gotten worse since then, as now it will regularly click on and off as the lights dim and whatnot. Our house has started doing this since... I would say late October or something (lights dimming periodically, etc).
A couple of weeks after I got the replacement UPS, it will occasionally... let me describe the lights. There are 3 lights in a vertical column. The middle one is a sine wave, and the ones above and below that one are clearly "bad" waves. The middle light is always on and green, but as of a month ago, the one and top and bottom one will go on (either, not both) for periods of time, and they are orange. I dont quite know what this means about my UPS.
So I'm thinking that maybe the problem is the house, but I dont understand why this would have only started happening relatively recently, and it was fine for the first month, and just got increasingly worse.
I just want to know as much as I can find out before I call PGE or excessUPS or the handyman, etc.
you can probably reference APC model SUA1500 and check out the documentation for it.
those LEDs you are seeing are for boosting and trimming voltage. it most likely means that you are seeing low or high incoming voltage to your household so the UPS is using its internal transformer to boost or trim the voltage to make it closer to the nominal (expected) household voltage of 120v. this is a feature of the UPS and yes, it the transformer can buzz. it is seen a lot in the summer with brownouts and sags and spikes, which are common power problems.
here is the user's manual for the SUA1500 which is most likely a similar model if i had to guess -> http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=SUA1500&tab=documentation
that way you can reference the documentation for the icons on the front panel, etc
also, it is common to see this when maybe a high current device powers on, such as an air conditioner or something on the same circuit that will draw a lot of current, causing the voltage to go down, and then the UPS boosts to make it higher. i realize you may not have an AC now but it could be a refrigerator, etc