My MacBook displays lines in the middle of the screen when scrolling up and down in the coloring app from the app store and I notice in other apps as well. When watching Netflix in HD or any videos in general I don't notice any lines it's only when I use certain apps that require scrolling. The line is one horizontal line in the form of a very tiny string going straight from one side to the other. When I scroll the screen splits in half due to the very thin line that's barely even visible. Thanks for your help.