Unless I reset the NVRAM, there is a screen hiccup at startup. Right after the Apple logo, but right before the blue screen, there is a graphics glitch where there are a bunch of gray lines/marks for a second, then it starts up normally. Could this be a virus? It goes away after resetting the NVRAM. I did a clean install of OS X Snow Leopard to see if it would go away, but it's still there. I don't want to reset the NVRAM again because I don't like how the computer starts up at a bright setting.