|"....but strangely only happens when I minimize, maximize or restore windows ..."|
I have noticed some systems do that in XP under various circumstances when you have installed certain video cards. I think the noise - it's quite high pitched - comes from the video card. It may do that in normal mode but not in Safe mode or Enable VGA mode. I am presently working on someone elses's dual boot computer that does that in XP in some situations but not in Vista. In that case there's often nothing you can do about it, and it's harmless.
"Nvidia Geforce FX 5200 (Heatsink, no Fan and Upgraded from Nvidia Geforce 2)
Original PSU (Dell, I think)"
When you upgrade your video you may need to install a PS with more capacity as well.
Your power supply must have at least the minumum capacity required to support a system with the graphics card you are using installed, or the max graphics card you might install in the future.
(Onboard video - video built into the mboard - IS NOT A CARD!)
You can go to the video card maker's web site and look up the specs for the model - often under system requirements - the minimum PS wattage, and, more important, the minimum amperage the PS must supply at 12v is stated. If you don't find that, any card with the same video chipset including any letters after the model number has very similar minimum PS requirements.
(This applied several months ago:)
If you want to cover any possible video card, a minimum 600 ot 650 watt power supply will handle any current high end video card, or even a X2 card (two video chipsets on one card) or two cards in two slots.
You can usually replace it with any decent standard sized standard ATX PS that has enough capacity, or more.
Standard (PS/2) power supply size - 86mm high, 150mm wide, 140mm deep, or 3 3/8" h x 5 7/8" w x 5 1/2" d , or very close to that, though the depth can be more or less for some PSs.
Don't buy an el-cheapo PS.
See response 3 in this:
If you have a sound card in a mboard slot it may be picking up electronic noise from the video.In that case the sound usually goes away when you uplug the speakers, or turn down the speaker's volume all the way, or mute the speakers in the sound mixer settings - try installing it in a different slot.
If you have an audio cable plugged into the back of an optical drive, it may be picking up electronic noise - you don't need that cable for more recent optical drives - the audio that cable provides is also available via the data cable (it's not needed in order to play standard audio CDs).