I recently (about a month ago) purchased a 13'' aluminum unibody MacBook. It was the starter model with only 160gigs HD and 2gigs RAM. I decided to upgrade both, increasing the HD to 500gigs (still the same RPM though) and the RAM to 4gigs (same DDR3, same clock speed). Since then several times now I've had the machine completely lock up and freeze with a graphical glitch while using OSX; it looks like bands of color streaking across the screen, flashing back and forth. It's kindof hard to explain but it's a clear "oh ****, something's broken." The first time it happened I thought I had seated the RAM incorrectly somehow since it was tricky to install (even though the machine recognized the four gigs) so I took the chips and replaced them and everything seemed fine. When it happened again I ran a RAM memtest which passed perfectly. It's happened for me doing the following things: patching the World of Warcraft client (but oddly not while playing WoW) and when I was running Second Life fullscreen (but somehow running SL windowed with EVE and WoW open didn't cause it.) I'm not really sure what the issue is, since a stress test didn't make it mess up either. I'll also point out that these issues don't happen in Vista at all either, even when I tried to kill the machine by running a stress test with two instances of Second Life, WoW and running a HD movie in iTunes all at the same time. Given the streaking seems to be some sort of video card issue it's making me wonder if it's a voltage problem since the upgrade that comes into effect because OSX has more aggressive power management than Vista, but I don't know how I can change any of that. It's also the same type of RAM and same HD, only both are larger, so I don't know why they would draw more power. I'm going to try to take out one of the 2gig RAM chips and replace it with the original 1gig (so I have 3gigs instead of 4) and see if that helps, and if it glitches again I'll go down to 2gigs next. But has anyone had this happen before after upgrading their machine?