IC's and Capacitors will sometimes emit a high frequency squeel, especially if they are bad or about to go bad. If you're interested in finding out for sure what it is before it pukes, open your case and try to listen to get it down to a section of your motherboard. Head down to your local electronics store and pick up a can of freezing spray. Then spray individual components while you hear the squeeling. When it stops, you've found your guilty IC. Write down the P/N and email your motherboard vendor asking them what they think you should do. It may be nothing, or it may mean you're about to lose your motherboard. Of course, if the sound is coming from your HD, CPU fan, etc., you should use your best judgement and notify them instead. If its coming from your monitor it probably means there's a capacitor about to make a big smelly cloud of colored smoke. If you're lucky you might even get to watch it bury itself in your cieling. =) Just kidding, this usually only happens when you reverse the polarity and power it up. I once saw the aftermath of a 2" diameter capacitor blowing completely through the plywood roof/floor of a mesonene above a co-workers workbench. It also burned the etching right into his workbench surface and splattered melted solder all over his work area.
Most fans can make high pitched noises, and most drives can make them too. IC's and capacitors (as mentioned) can be guilty as well. Try and work out whether anything in your system has changed in the last few weeks (hardware-wise) and this is probably the guilty party.
Otherwise, go with the solution above, although be careful where you spray the stuff (i.e. don't spray it in a fan, cos it will make the fan cease up!).
~ I'm not AMD biased, I just think their chips are better. ~
You are about to answer a thread that has been inactive for more than 6 months. If you still wish to proceed, please ensure that your posting is original and does not duplicate or overlap any prior responses to this thread.