I recently experienced the same issue, it happened after I did a routine clean up of the ventilators. All the pervious suggestions: pressure points, gfxCardStatus, software updates, etc did not solve the issue. When I use an external monitor the issue does not persist, which makes me think that it is input/output or motherboard related. Would anyone have a potential diagnosis? Is it that I accidentally short circuited something while cleaning?
Any tips are much appreciated.