Adjusting the Speed of the Video Card Fan
The fan used to cool the GPU on a video card is often times the loudest in an entire system. Modern GPUs are extremely powerful pieces of hardware and require a significant amount of cooling in order to remain functional. Sometimes, however, the cooling provided is a little more than needed, and room for moving the fan speed down can result. Obviously, a GPU which is already running at a high temperature should not have its fan speed limited, so be careful to check how hot the GPU is running before limiting the fan speed. Also keep in mind that some video card manufacturers consider a warranty void if fan speed is tampered with.
There are a lot of different programs that can be used to adjust fan speeds, but Rivatuner is one of the best. It is compatible with both Nvidia and ATI video cards and it has a robust interface that includes accurate reporting of GPU temperatures and fan speeds. Download and install Rivatuner, and then launch the program. Check the GPU temperature with the Hardware Monitoring tool. In general, a core temperature of 90 degrees is the limit, but you should check while playing a game or otherwise heating up the graphics card. If you have some headroom, you can turn the fan speed down: from the Main Menu click on the button directly to the right of the "Customize..." text. A small menu will appear with various options. The one furthest to the left will be Low-Level Settings. Select it.
Now there will be a menu with Overclocking and Fan options. Go to Fan and click the box labeled Enable low-level fan control. The slider will now be available. Click on fixed, and then move it to the lowest possible setting. This will be 25%. Once the fan speed is modified, be sure to monitor the GPU temperature with the Hardware Monitoring tool in Rivatuner. This will ensure that the GPU is not becoming too warm. Remember, a core temperature of 90 degrees Celsius is generally the limit, but air cooling is heavily dependent on ambient temperature, so keep monitoring: what works in November might not work in June.