Heh-heh, I guess if I perfectly knew, then I would perfectly know where exactly my own one does come from.
One thing that can help you is removing the current video card, and put another thing(s) that takes the same (or more) wattages from the PSU, like another video card or harrddisks+usbs-in or whatever. And if the sound persists, it is the PSU. You said you did not have this sound before.
Another is with a sensitive sound amplifier, I don't know if your microphone is of good quality. But, there is the sound conductivity that might make things difficult.
Anyway, apart of it being a bit irritating, there is low chance that something is soon gonna break, but, like the guy told you, monitoring software can help if there is pending damage, error or something.
You can also see if some fan is hitting onto something there.