I have a 2013 15" rMBP with Iris Pro and Nvidia GForce 750m. I've noticed that this model is more delicate in terms of bumping the thunderbolt cable could cause an external monitor to become snowy. Well I was working with two monitors when my external suddenly became snowy. I unplugged it and my screen blinked like normal to switch back to the iGPU. Then I plugged my external back in and my screen when black and stayed that way. My iTunes was still playing so the system was running, but the screen was black. I couldn't put it to sleep and I had to force shut it down and lose a lot of work. Is this normal? I am running gfxCardStatus, could that have done it? For the sake of full disclosure. I had my system set to iGPU only. After I plugged in my monitor I remembered to switch it back to dynamic switching and the external came on. What scares me is that I never bumped my monitor cable when it when snowy. Any thoughts? Edit: by snowy I meant all white nose.