When my computer is turned off after using it I can hear a very faint buzzing noise from my Seasonic X-660. If I turn off the mains power I can hear the noise slowly dying down. If I switch the PC back on the noise is not present anymore. I got this power supply a month ago. I don't think I would be able to return it because the store that I bought it from wouldn't have the silence to test it in and had even failed to test my other Corsair HX650V2 while Corsair confirmed there was a problem. Is this noise normal?
You need to RMA the unit right away. Some caps can make noises during charge and discharge but it is pretty rare and only very high loads. The coils on the other hands make the buzzing sounds even at low loads but especially audible at high loads. To make things short coil squeal could also be the sign of a defective unit if it is having the squeal through out the day and very often. It can kill the unit if happens to short any where in the coils.