Depending on your RAM and the number of apps open the MB could just be swapping to disk. Normal memory management and nothing especially to worry about. The fans on my MB always seem to be somewhat erratic. Once they didn't kick in until an indicated 91C!! Most often they will run at around 50C+ you should ensure there's adequate airspace around it when using it - a tray etc will be fine, but on your lap its likely to be overheating constantly.