[Carolyn (OP)]

For the last 4 or 5 hours, my desktop pc has been sort of 'singing' every half hour or so.  Sounds like it's singing 'balah tee daaa'.  I've been using my lap top this evening, so every time it happens I'm not sitting there.  I haven't found any error messages or anything that looks strange.

Any ideas why it's doing that?

[RD]

If the computer is on, but you've not touched it for say 10 minutes, it will look for things to do like scan for viruses or download updates for your software. These housekeeping tasks may be the responsible for the "singing" when you're not at the computer.

A less likely explanation is a virus/malware using your computer.
If the "singing" is a new phenomenon, and it continues to occur "every half hour", then best do a scan for malware.

[BenV]

It could be the sound of the hard disk spinning, which could be for a number of reasons - one question though, how long have you had the pc for? If it's close to 5 years, I would recommend getting a new hard drive and backing everything up, as almost every hard drive I've owned gave up the ghost within months of it's 5th birthday. Often this would be preceeded by it making new noises.

[turnipsock]

It'll be the cooling fan.

[Flyberius]

I would put my money on the hard drive.  I have seen this problem before and will end in a hard drive failure.  Bcak up now and get a new hard drive or you will loose all your data.  If its your fan give the thing a clean out with some unlinted cloth and if you can use some of that antistatic spray to get dust out of all the nooks.

I moved to water cooling to circumvent the noise my PC used to make.  Now if you really listen you can hear the pump humming away.

[RD]

I moved to water cooling to circumvent the noise my PC used to make.

Do you need to add anti-freeze in the winter ?  []

[Flyberius]

I think it is anti freeze