I have a Compaq Presario PC I bought nine years ago and it has been a fairly good computer. The exact model number is: SR 1913WM. I recently had to install a new hard drive and since then while the computer is in use, my processor fan will start running on high for a few minutes and then will go back to running at a lower speed. It just continually runs through this cycle of high and then back to low. The fan will continually run on high while the screensaver is going and also while playing games. Any ideas? 
Typically, computers work harder when performing certain tasks such as gaming, downloading music, or downloading pictures. When this happens, the processor fan also works harder. Since you recently swapped out your old hard drive with a new one, it is possible that the computer must now work harder when booting up due to the size of the hard drive. Try the following suggestions to see if you can resolve the problem of the noisy CPU fan. Since the fan noise is associated with your computer’ start up and resource- hogging activity such as gaming, it is likely that nothing is actually wrong.
Troubleshooting Noisy CPU Fan: Overheating
An accumulation of dirt might exist leading to overheating or even have been dislodged while you installed the new hard drive. Disconnect the computer from the power source and check for dirt. You can use a can of compressed air to remove any dirt or dust that you find. Additionally, you need to make sure that sufficient space exists around the computer to avoid overheating due to blockage of the air vents.
Troubleshooting Noisy CPU Fan: Physical Set Up
It is possible that you dislodged either the fan or the cables inside the computer when you replaced the hard drive. If this is so, the cable could be hitting the fan or the fact that the fan is ajar could be causing the noise. Disconnect the computer from its power source, open the case, and check the fan out to see if you can see any physical problems.
Troubleshooting Noisy CPU Fan: Heatsinks
It is possible that your computer’s heatsink is in need of adjustment. The heatsink is responsible for attracting and dissipating the heat within the computer. It is attached to the processor and is responsible for getting the air properly distributed with the cpu fan. If your heatsink does not have a sufficient amount of thermal compound on it, it can function improperly. This compound acts as a seal between the heatsink and the area of the computer that it is responsible for cooling. If you do not have enough thermal compound on the heatsink it is possible that this is responsible for the added noise. Check it out and add a fine layer of the thermal compound if it is needed. This is a tricky process, so if you aren’t comfortable with it, you should get someone else to deal with it.
Troubleshooting Noisy CPU Fan: Faulty Fan
In some cases, especially when all of your troubleshooting has not resolved the problem, the only thing left to do is to replace the fan. Fans do stop working and a noisy fan could be the first sign of this.



