I was working in the computer area one night. Of four computers, I was using two, one had been shut down for the night, and the last had been left on, but was unused.
Suddenly the room was filled with a very loud noise. We are talking quite loud, almost like a fire alarm - uncomfortably loud to the ears. My first thought was an alarm on the UPS. I checked it, and it was fine. Then I thought maybe a fan bearing gone bad on one of the computers. I shut down the one not being used. Nothing. So then in spite of losing work, I felt it urgent enough to immediately shut down the two computers I was using. Nothing. So my next thought was fans in the room. Shut them down - nothing. Then I thought maybe the lights. Nothing. So my final thing was to unplug the computer that was already shut off - Bingo!
What a surprise. I wasn't sure if the noise was from the computer or from the surge protector it was plugged into, so I ran an extension cord across the room. It ran fine about 3 days and then the noise came again, not quite as loud this time, but still loud.
So I am thinking power supply or motherboard. The frequency and texture of the sound is the same as the squeal you get from the computer when you disconnect the power and the electricity drains from the system, except that that sound is mildly soft, but it gives you an idea of the nature of the sound. So I'm thinking maybe the motherboard is alarming me about something, but why so loud? And why continuous and won't go off until unplugged? Or is this a kind of sound a bad power supply can make? This power supply is the one I recently put in my Soyo Dragon Ultra 400+.
Any input appreciated.