Strange sound...not sure what it is

[bikinpunk]

I built my current computer about a year ago using pre-existing harddrive & optical drives, but everything else was brand new. Just today when I turned the computer on it started making a strange sound. It sounds like a battery-powered device dying (when the battery goes dead). Think of an electric shaver going dead; that's the same sound I hear.

I tapped on the back of the case in a couple spots and it has stopped, but I have no idea what it could be. My gut is telling me it's the harddrive since that's the only moving part I can think of, though my computer seems to function normally. Any ideas?

[juppy]

More likely to be a fan than the hard drive. You can test for noise in fans by getting a small wooden dowel rod and putting one end on the fan shroud (the outer area around the fan....not the blade itself) and the other end up to your ear while they're running. The noise maker will have a much louder sound travel up the stick. Check any case fans, the heat sink fan on your processor, and even the small chipset fans on the motherboard. Could also be a fan inside the power supply too, but those are a little harder to get to.