I have a very noisy fan at the back of my pc tower. It spins to fast and therefor makes to much noises. There are various ways to reduce a fans speed and one of them is using the free software speedfan.
Speedfan scans your system and detecs fans automatically. It also shows temperature levels for system devices, for instance hard drives. To cotroll a fan you reduce the value of that fan from 100% (fastest rotation) to a lesser one. The changes take effect immediatly which means you can hear that it becomes more silent. Mine was close to being complete silent by 50%.
[tags]speed, fan, speedfan, control fan, software, temperature[/tags]

Use Speedfan to control temperatures
Analyzing drive health with SpeedFan
Monitor CPU Core Temperatures