LAst night while playing with my iBook.. I heard a loud whiirrrr and whizzzz coming from the top of the machine.i.e the part closer to the screen when opened. It soudned like the harddrive or the fan going in full gear. My iBook is about 4 months old and have never heard anything like it before. Granted it was very hot to touch at the bottom and I hadn't rebooted or shut it down in at least 3-4 weeks. I usually just put it to sleep. It sort of got me worried about whether I should be shutting down my mac or at least rebooting it every once in a while to keep things sane..? I am a switcher so this is a fairly normal occurence on Windows boxes. Any thoughts? Thanks!