|Visually look for a wire or something leaning against a fan. Look inside while it is running to see if you can narrow down where the sound is coming from. Make sure that you have the machine off before touching anything inside of the case, then touch a metal part of the case (to ground out any static potential you may have), then unplug it. Loose wires should be tie banded in place to prevent this sort of problem, left unfixed can wear through insulation and cause other problems. If the sound is coming from a hard drive, verify your back up and since it is still working, make an image of the hard drive to an external hard drive ASAP. Then make a Windows 7 Repair Disk (Note: I just saw you have Vista, i think it also offers this option in the back up section but I am not sure), then purchase a new hard drive. If the drive still works, you can clone the drive to a new one directly, but if it does not continue working long enough, you can use the drive image to restore it to the new drive with the help of the repair disk (If Vista does not have the disk image and repair disk options, you may want to use another program to do this. Acronis and others are available, Western Digital offers a free version of Acronis if you have or purchase a WD drive.).|
You have to be a little bit crazy to keep you from going insane.