Chirping sound

I am running Windows XP Pro on a 233mhz (pentium 11)with 320 mg ram. I have had it running for quite some time, but recently I have started hearing a single chirp noise coming from my PC. nothing seems to happen when it chirps, but it does it very speradically, with no noticable pattern. I would like to know if anyone knows what this sound means, and is there any damage associated with it.
I have never come across this sound before, and can find no reference to it anywhere.
Thanks in advancefor your help!
Jeff McKay