1. "Small Cooling Fan" system impedance: range between a chassis air inlet and outlet of the total system impedance of 60-80%, while the greater air flow, noise is relatively higher. System impedance is higher, the greater the airflow required for cooling, so in order to minimize the noise, the system impedance must be minimized.
2. "Small Cooling Fan" disrupt airflow: spoiler along obstruct airflow path encountered caused generate noise. Therefore any obstacles, particularly in the critical range of the air inlet and outlet must be avoided in order to reduce noise.
3. "Small Cooling Fan" speed and size: Due to the high speed fan noise greater than the low speed fan, so you should try and use low-speed fans as possible. And a large size, low speed fan, generally, quieter than the small size, high speed fan when transporting the same air volume.