Thermal performance is the most important issue to be considered when a thermal module is designed for a notebook personal computer (PC). Because the fan causes air-borne noise and affects the user’s comfort, the acoustic characteristics of the module attract more attention. Experiments were conducted to study the noise sources, the noise characteristic and the main factors influencing the noise level. The difference between the air-borne noise of the thermal module and the whole computer system was analyzed and its propagating characteristics were derived. The influence of I/O ports on the air-borne noise was also studied experimentally.