It's either your background image or ( hopes not ) the GPU has issues. You might get an idea by running the AHT but I'd experiment by editing that background first.
It even appears at boot before the Apple appears.
I'll run the AHT now, just wanted to know if someone knew what would specifically would cause that.
EDIT: I couldn't get AHT to run?I held D and it sounded like it was looking for it, and then just booted into OS X when it couldn't. Tried about 10 times.
Are you on a 2011 15"/17" MBP? If you are, it means that your MBP has succumbed to Radeongate (the GPU failure that affects every single Sandy Bridge MBP logic board with the Radeon GPU).
There is no real fix to this as every Sandy Bridge logic board with Radeon has this manufacturing flaw that causes the GPU to fail. The only best temporary way is a GPU reball/reflow.
Sadly, I am on a 13" with Intel HD Graphics 3000.