Hey, I've noticed (actually the past few months, but it never really annoyed me until recently), that my left fan will spin really fast and very loud a few times during the day at random moments. Sometimes I will leave my computer for a few minutes, and it won't be doing anything difficult (just finder, or something not cpu intensive), and it will be blowing like crazy when I come back. These "episodes" last for a few minutes and then return to normal. Activity monitor shows that my cpu is barely being used, so nothing is taxing the system. Weirdly enough, when this happens, istat says the fan is at 0 RPM, yet it is very loud. I cleaned out my fans with a little keyboard vacuum to make sure there was not dust stuck in their, but it still makes those fan noises occasionally. I even did the Apple hardware test, and nothing showed up. I have a late 08 MBP.