I've had my 15" 2011 MacBook Pro for about 6 months now, and I picked up a VGA adapter for it a few weeks ago. (Thunderbolt -> VGA)
I have the laptop in clamshell mode running an Acer monitor, and will occassionally (every 5 minutes or so) experience a weird flickering, as seen in the first few seconds of this video:
I see the weird flickering/distortion, but it doesn't last nearly as long as shown in the video, it's maybe 0.25 seconds of "shaking", then back to normal for another 5 minutes.
I experience this issue with multiple different VGA adapters, so I'm convinced it's a GPU/port issue.
I've installed all the EFI/SMC/Thunderbolt updates available in Software Update, but I've heard that there was a separate firmware update being passed around the Apple Discussion forums, but not released publicly.
My question, is whether I should take this in to an Apple Store to have it checked out, or whether there's a firmware update I can install to test? I've seen firmware updates for cinema displays, EFI updates, etc. but they haven't fixed my problem, so I'm wondering if there are any last efforts I should try before scheduling an appointment.
Edit: I'm not using an Apple adapter, but a Monoprice version. I have used a friend's Apple adapter however, and the problem continued to occur. Also, I'm running Lion 10.7.2