I have a MacBook Pro mid 2012, and I've noticed lately that I've been having this issue while watching YouTube videos: Not only does it show those on my desktop, but there will be a black line across my dock and it flickers. I click down there or hover my mouse over it and it goes away otherwise I'd have a screenshot of that too. I read that it could be kernel panic. I was told to reset my NVRAM, which I did, and also ran a boot diagnostic and it said there were no problems found. At this point, I notice that the only time this happens is when I'm streaming video for awhile. If I'm just doing light browsing everything is ok. Does anyone have anymore suggestions at how to fix this? Thanks.