Loud Squealing Noise

IT sounds like a fan may be going bad on you. The bearings in the fans can make that kind of sound when they wear out. I would check your fans. While its running, use your finger or something small to stop each one for a second or two and see if the sound stops.

This may also be a HDD wearing out as well, though its doubtful. I would think that the drive would stop working or booting at all if that is the case.

Fan or Hard Drive. Do not disconnect the fan from the CPU heatsink, since most motherboards that are higher end will not turn on when the bios does not detect that fan.

When blowing units out, you should only use higher pressure such as from an air compressor if you have pulled the Motherboard and power supply to get the dust out of them. I always turn the pressure down when I use a compressor. Fans can end up showing failure when you get the crud cleaned out of them in the same way that a vehicle engine does when you get the oil and crud cleaned off for a minor engine repair.

kipper said:

Yes, that is why I mentioned "case fans"...........I doubt it is a HHD noise, they usually sound more like shaking a small box of rocks......

Actually a failing hard drive sounds like a squealing noise not like a bunch of rocks shaking when the bearing starts failing. When the heads start failing, you hear a slapping noise from the arm going back and forth. When you open up a drive, you will see the track marks across the platters.