if it's getting louder, it probably means that you have a fan that is failing. Some lower quality fans have a mean time before failure of 20,000 hours, and even cheaper ones may be so low they can't even claim that. If you've had your computer for a couple years, it's probably a fan dying. You could try to clean the blades and housing, that might fix the noise short term, but a new fan would be better. One exception though, if it's the power supply fan that's going out, don't try to change it out. Just get a new power supply unless you want to risk damaging your computer.