As has been said, it's either the ribbon connections or a few of the output transistors on the driver chip that drives that portion. it's possible that the ribbon cable is delaminating from the edge of the LCD, and the problem will spread and get worse. If you're good with working with small things, you could take apart the screen and press the ribbon cable on that edge on that area down and see if it goes away. Otherwise, ignore it and think about using an external monitor...