Time to pop off the case cover and try to isolate the origin of the noise. My suspect---a cooling fan.
OK, first of all you need to know that I know how to use a computer but no idea how to fix anything. I have an emachines brand T2484 with Windows XP, 2.40 GHz intel celeron processor, 80 GB hard drive, and i don't know what else. My problem is that when I turn it on, the pc makes this long, drawn-out screeching sound that goes on for minutes (it sounds a little like microphone feedback). It's almost ear-piercing and it's driving my roommate and I crazy. I've had it for a year and it only started doing this recently. Earlier, when it started making the noise it would also do it randomly while I was working on stuff, but now it only seems to be on startup. And turning the speakers on and on has no effect. Please, anyone have a suggestion?