"24V DC Cooling Fan" hard noise: the sound is mainly hard clear sound Kaka Lo, the poor quality of the hard disk will sound relatively large, there is too much fragmentation will increase if the hard work so hard bigger sound, but also there is a situation that is hard disk bad sectors, and will lead to increased hard disk sounds. "24V DC Cooling Fan" in normal operation, there will be some noise at work. But these voices is small and hard to read only when the data will be generated. Dust accumulation: chassis, power supply, CPU heatsink to accumulate large amounts of dust can also cause increased "24V DC Cooling Fan" sound you can try using a screwdriver to slowly turn the power supply installation commissioning a few screws on the chassis to see if there. look at the effect of deformation of whether the chassis layout, if there is a change, the source of that noise is likely to be the power supply, CPU fan.