Just got back from the apple store to take my macbook to get checked out cause it has this weird flashy thing at the corner of my screen when ever im on youtube or use certain applications. Anyways they told me that the app dock is causing it so they told me just to hide the dock. I was pretty unsatisfied with that answer, they just found a way for me to go around it but i believe it shouldn't even be happing in the first place. What do you guys suggest i do?