I just got the MBA 11" Ultimate today, and it seemed fine all day. When I opened it up this evening in bed, I could hear this annoying buzzing sound coming from the back-left side. I'm assuming it's the fan, but it's driving me nuts - it's not even loud, but I can hear it clearly because it's so quiet in my bedroom at night. Is this expectable/normal? I don't recall any of my macs before doing this - either they had a loud fan when it was necessary, or i didn't hear anything at all. This is just a distinct annoying buzzing sound.