XBox 360 Two Red Lights...?

So i have the two left lights blinking red on my 360. xBox.com site said it was due to issues with overheating. I had already moved the system to the top of a wooden speaker housing and between the two a thick slab of granite sized just right to not block the air vents. When the problem persisted i looked at forums, they suggested keeping the power supply cool and moving the system so it used its own outlet. After doing all of that it has only extended the delay from five/ten minutes to more like twenty/thirty. It occurs occasionally when i play a DVD and when it does it takes, normally, at least an hour. So does anybody have any other suggestions? This is really annoying as i can play games just long enough to think it wont turn off, then BAM it has to cool off for about an hour.