The squealing has happened twice under similar circumstances. I was watching Planet Earth from bed with my headset on for sound and I tugged on the cord and there was no more slack so it kind of jerked on the back of the computer (it wasnt hard at all) and then the squealing started. I restarted and the video wasn't working. I reseated everything and then restarted and everything was fine again. It happened again today when I was in the back plugging in my webcam. The squeal started after plugging in the cam to the back and I restarted and didn't get video. Opened up the PC, reseated, and it booted fine.
NOTE: When I didn't reseat anything it would just not receive video. I tried restarting a few times and it would NEVER get video until I reseated.
I'm just curious what this is so I can fix it! Is it a loose video card/sound card? Something on the mobo shorting?