Screeching / EERRRRRR then Lockup / reboot.

Ok the problem is I can play on the computer for hours with no problem or minutes and this happens. It can be something as simple as watching a video on youtube or playing a full screen MMORPG. The system locks and the screeching or wierd noise happens at the same time it's not the same audio that was playing it's not a repeated noise. Sometimes when it happens it will screech for 10 sec and then restart and sometimes it will just keep going and I'll have to hold down the power button. It was happening before and after these upgrades. PSU, Graphics card. I have swapped the hard drive with another and it still happened. I am in the process of ordering some more ram and when I get the new ram I'll be taking all 4 x 1gb sticks out and putting in 2 4gb sticks. Oviously I've formatted and reinstalled since I've tried multiple hard drives. This problem is also accompanied by random restarts. I've turned off the automatic restart option in system setting and it still happens. It's not the kind of restart that happens from an error or lock up. It can happen during any type of status, Idle, intense usage, web browsing and anything. I just reformatted and turned off windows updates to see if it was being caused by a hot fix or patch. I've tried running all types of memory test hard drive test I can find anything that would cause an integrity issue or error. I cant make it happen on command but It will happen every day atleast once. The graphics card has the most up to date drivers I've also tried older versions. I'm pretty good with computers but I cant figure this out. As far as cooling I have the side of the case off and a 20 in metal bladed fan pointed into the pc. It happened before and after the fan was there. I'm not overclocking my graphics card.
Please help
I'm sorry but as I went through typing this up I wrote what I thought of so it's all in random order.

Thank you in advance
Derek