Saturday evening, my 9 month old MacBook started running far hotter than normal, and the fan running 4000 to 6000 RPM almost constantly. This obviously decreases my battery time to <2hrs from it's usual 4+ hours. This is all while the computer is just sitting there doing nothing, "at idle" if you will. Of course using applications makes it even worse. It's never acted this way in the past, even under heavy use the fan never ran like this. All of my searches are only bringing up references to MacBooks being inherently hot, but not giving me any clues as to what has caused this sudden change. I have not recently added any applications, the software is up to date. Any ideas?