Using my 2012 Retina 15inch MB Pro and an iPhone hotspot.. I just confirmed the described issue, in my case, is associated with WiFi. I turn WiFi off (on the Mac) and the flicker stops. It doesn't matter if the hotspot is enabled or not on the iPhone. I turn WiFi on and the flickering starts again in seconds. I don't see a need to replace motherboards and displays as other than the flickering everything works fine. It sounds like a firmware or software update associated with WiFi is in order... Can the super techs at Apple confirm this?