I recently purchased a Cooler Master Silent Pro Gold 800W power supply, and it has worked perfectly except for one issue.
Randomly, at intervals of at least four hours, the PSU emits a distinct buzzing sound that lasts for five to eight seconds. This occurs even when the computer is off (though it is still plugged in with the PSU power switch on), often a few hours after the computer is turned off.
It is highly nerve-wracking, as I don't want anything bad to happen to my machine. Is this something I should be concerned with? What could be the cause?
If the sound is electrical arcing, it is unsafe to use. You may be hearing the 'crackle' of a poor electrical connection inside the PSU. When the PC shuts down the PSU, there is still live electrical connections inside the unit unless the 0/1 switch is turned off.
If the PSU is still under warrenty, I would return it. If it is passed warrenty, you may be able to open it and see where the problem is occuring and repair it. But that would take some familiarity with electronics.