Fans get noisy often because of dust collecting on the blades and around the heat sink.
May be worth taking side off the PC and either using a can of air blasting the fan and processor heat sink. (You could try a straw and blowing hard but more moisture involved or very gently cleaning with a q-tip or similar)
You could also try Speedfan to see if you can gain control of the fan speed itself. Just beware adjusting it too low and causing the processor to overheat. click here