tt400 wroteTurn off your PC and confirm that the PSU is buzzing. Leave it alone for a few minutes and come back. If the buzzing is gone after a short time, it means it's perfectly normal. It takes time for the electrical charge to wear off. It's called coil noise.
EDIT: Just read your post again and saw that you already know what coil noise is. So don't be worried.
It just stopped doing it altogether, my PC has been on for about a day and a half and I have been listening to it frequently and there are no signs of buzzing anymore, I ran some benchmark tests for about half an hour to stress my system and still no buzzing.
I'll notify if it ever does it again, maybe it has to do with the outlet itself, I'll just wait and see.