This isn't so much a problem as something I have just noticed. Everyone in the house is asleep, and for once I don't have headphones on. When I use two-finger scrolling on my BlackBook, there is a strange... almost purring noise from my machine. It's extremely quiet, and I can only pinpoint it to the kinda under-keyboard-towards-hinge area. It is loudest when I scroll on pages with a lot of dark/light alternation on the page, and quietest on plain light pages. It really is quite odd. Am I making my Mac purr by scrolling through all my regular webcomics?