is this only during boot or at the login window or does it happen post login as well? if it happens post login, take a screenshot and see if the artifacts appear in preview or it the image looks normal. if its only happening during boot and the aht gives you a clean bill of health might be worth a shot to reinstall loin
This only happens during boot and login window, have not seen any artifacts post log in.
( The only other thing that is a little weird about the machine is battery life seems short going to run some tests on that to see what happens, but even with energy saver settings, airport off and so on seems to be more in the range of my other non-Unibody laptops of 2-1/2 hours. maybe 3. Though I did not expect the full 7, thought it would be more, though I would assume unrelated.)