The CPU fan in my system is constantly changing speed. If it just ran at one speed (like very fast) it would not be annoying, as it is the change n sound that makes it's presents known.

Is there any system setting to adjust whatever is changing the fan, or do I just need a new CPU fan?

 

Depending on the computer, you may find options in the BIOS. When you first start the computer up you should see an option to enter the BIOS by clicking on a particular key. Most computers are the "Del" or "F2" or "F10" key. Your computer will tell you when you first start it up. You could also look into your owners manual or check the manufactures website for info.

 

check SpeedFan, it comes with some settings that may not be available elsewhere.

 

The speed of the fan is to cool down the heat sink on the cpu. If the heatsink is full of dust, it get quicker warm, and the speed of the fan is fast. If you use programs that doesn't require much, as in surf the web or checking e-mail, the speed goes down. And if you then start a game or something, the CPU needs to work more, and is getting warmer -> speed goes up. I would first check for dust, fur and ants.

Guess it is a stationary computer.

 

if you are using compressed air to blast dust out, hold or lock fan to prevent it from spinning (to prevent backfeed that may damage other components).

 

just put music on.. (and headphones)

 

If your fan is in good condition it will run accordingly. When the processor executes low volume progamming instructions the fan fan will run in comperatively lower speed. When the processor executes a large number of instructions and if all the parts of the cpu actively working like running a game then the fan speed go fast. This is for cooling the processor and cpu parts.

If this is not the case then you can seem that you fan becoming worse. So, You can change your fan. you can learn more from bellow:
http://www.techyv.com/questions/my-cpus-fan-very-noisy