These computers were made to be used on a flat surface bad examples of low airflow surfaces are Carpets, your lap, hot surfaces or surfaces that trap heat such as a blanket. A flat surface such as metal surfaces, cabinets, or tables creates more airflow along with allowing the heat to move to the cooler surface from the metal computer case pieces. If the fan starts blowing loudly it means there is to much heat and not enough airflow. This can mean two things one there is something preventing air from exiting the case, or two there is something sending false temperature readings to the computer.