A noisy CPU fan can be a nuisance and may indicate an underlying issue. Firstly, check if the fan is dirty. Over time, dust and debris can accumulate on the fan blades and in the heatsink. This can cause an imbalance in the fan's rotation, leading to increased noise. To clean it, turn off the computer and unplug it. Open the computer case and use compressed air or a soft brush to carefully remove the dust from the fan and heatsink. Make sure to clean all the nooks and crannies.

Another possible cause is a loose fan. The fan may have become loose due to vibrations or improper installation. Check the mounting screws or clips that hold the fan in place and tighten them if necessary. Sometimes, the fan bearings can wear out. If the noise is a grinding or squeaking sound, it could be due to worn-out bearings. In this case, you may need to replace the fan. Lubricating the bearings can sometimes help. Use a small amount of a suitable bearing lubricant, but be careful not to overdo it as excess lubricant can attract more dust.

The fan speed may also be set too high. Some motherboards allow you to adjust the fan speed in the BIOS settings. Enter the BIOS and look for fan control options. You can try reducing the fan speed slightly, but make sure not to set it too low as it could lead to overheating. Additionally, check if any software is causing the fan to run at full speed. Some applications or system utilities may have aggressive fan control settings. Close any unnecessary programs and see if the noise reduces. If the problem persists, it could be a sign of a more serious issue, such as a malfunctioning motherboard or a problem with the CPU itself. In such cases, it may be advisable to seek professional computer repair assistance.