Joshua Farnell since this happens after the TV has been on for a while it could be a capacitor issue as well as a transistor issue on the main board. Try to run your TV with the back off and a fan circulating air against the main board. The other thing you can try and do is use some electronic freeze spray and spray small parts of your main board while your TV is doing this. See if that corrects the error and post and image of the main board and mark the area that showed improvement.
There is always the possibility (very minute) that this an issue with the actual panel. Without an oscilloscope and schematics, it would only be a guess and can only be verified by ruling out the main board.