Unusual hardware alarm - please help

This weekend my PC began to give an alarm sound, a couple of times during use and once when idle (but before it had gone to standby). It was not coming from the sound system; I think it was from a piezo, but which one (mobo, GPU, or somewhere else) I could not tell.
All fans were running, and temps reported by SpeedFan and by nVidia's Control Panel were normal to cool. Nothing was written to the Event Logs for these incidents. There was no application or O/S crash. I didn't see anything unusual in the BIOS. On one reboot, however, I saw a couple of RAID detection messages, which is odd because I'm not using RAID.
It's a shot in the dark, but I'm going to replace the CMOS battery, although I've never heard of a low-battery alarm.

Any thoughts on what this might be? System is described in my .sig.
Thanks.

Usually mobo give beeps not alarms. The alarm does sound like the UPS. The alarm on my APC UPS went off one time and it drove me nuts until I figured out it was the UPS. I don't ever remember why it went off other than the battery was low.

A UPS will beep when the voltage at the wall outlet goes momentarily low. I hear these errant beeps every once and a while. In my old house I used to hear them quite frequently. It just means the UPS is doing it's job. I'm not saying that you're not due for a battery change. You can test by booting to a floppy, so not to corrupt the OS, and unplugging the UPS to see how long it stays up. Obviously the up time depends on the size of the UPS and the load but you get the idea.

A battery it is then.