Hye I have a mid 2011 27" iMac with Core i5, 24 Gbs of ram and 1 TB Solid State Drive. I noticed that my monitor does this flashing thing all the time. It will happen at various places around the monitor and if i move screens around or over it, it will usually stop for some time. It changes speed and also changes size on a random basis. Is this my video card going bad? I do have a second monitor (LG) plugged into it via lightning cable to HDMI, but i have unplugged it and rebooted multiple times to see if that fix the problem and it has not. Video is posted below on the link. Please Help!