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
Best Answer
Since your MBP is a 2011 (and we're still in 2011), I'll assume it's still under AppleCare 1st year warranty. If so, consider getting it checked at the nearest Apple Store. Do mention you tried applying the firmware update. The list of Apple firmware and SMC updates is here.
If you don't live near an Apple Store, and if you're curious, you could try to diagnose if there's a hardware problem using Apple Hardware Test (AHT) which is a software in one of the DVD that came with your MBP.