Before we begin, let's look at what causes noise in the home PC. Usually, the single noisiest component in the PC is the fan. This could be the CPU fan or another fan that is installed in the computer case to keep things call. Fans are the biggest culprit. The other contributors to noise include the hard disk drive and DVD drive.

The first and most important way to reduce the noise level in your home PC is to replace the fan in the computer.
 

Replacing the computer fan can cut down noise
 

The first fan that I try to replace is the fan attached to the computer case. You can easily buy computer fans for a cheap price and replace them. The CPU fan is something I recommend you do not touch, in case you affect the CPU. But if you're convinced the CPU fan is going a lot of noise, you can also buy a replacement CPU fan as well.

Now, another way to reduce the noise level in your home PC is to get a better processor. This might sound weird, but the truth is that when your CPU is slow, it causes lots of other components to chug along, especially the hard drive. That in turn causes heat build up, which forces fans to spin faster, creating more noise. So get a better CPU and reduce the heat and fan noise in your PC.

I'm surprised at how many home PCs get placed in hot environments, e.g. next to a window, or near the TV. Remember, one good way to reduce the noise level in your home PC is to place the PC in a cool environment. When you do that, you reduce heat build up in the machine and prevent the fans from whirring too much to keep the PC cool. As a result, your home PC will emit less noise.
 

Having the PC in a cool place helps cut down noise too