EL CAPITAN 10.11.5 I am trying to nail down the root cause of the problem. This is weird. There is white and black flashing on a small part of screen. It always happen on the left side of the screen toward to bottom corner of the screen. I can hop a mouse pointer over the area. I am not sure it is the video cards problem, OS, cable or what? I did capture the videos on my iPad. Please have a look. Have anyone experienced the issue? ***Update 2*** I can scope down and be able to recreate the problem. It only happens when I open 2 applications. One application must be iTunes application. To recreate the problem, all I have to do is to expośe iTunes application with another application back and forward constantly. I have changed the cable. But the problem is still exist.