Why is my fan turning on and blowing loudly?

The computer's fan is meant to cool down the cpu. Usually, the fan becomes loud when the cpu is over-stressed with a lot of programs. However, if the fan gets really loud for only a short period of time, then it is possible something might be wrong with the driver. Try reinstalling the driver for the fan. There are many programs online that you can install to control the fan speed; however, be aware that controlling the fan speed may result in your computer overheating. An occasionally loud fan may also be an indicator for a hardware problem where either the fan or the thermostat is malfunctioning. If this is a concern, refer to the Motherboard Replacement Guide.