Here's what Seasonic recommends when you encounter electronic noise with their supplies:
In the BIOS, the function of Audio Always On must be DISABLED as this does not conform to ErP standards.
As well, in the BIOS, all energy savings modes such as ErP/EuP, StandBy Energy Savings, S4/S5, must all be ENABLED.
I always have onboard audio disabled. I was only able to find ErP in BIOS while it doesn't look like S4/S5 don't exist for Haswell. Again it still seems to buzz, then goes away a couple hours later.
Have you found the source of the buzzing? If not, have you tried seeing if there is maybe a label or something or wire hitting the fan? I only suggest this because I had something similar happen and my graphics card was making a terrible buzzing noise but when i took it out of my pc it seemed there was nothing - when i replaced it, happened again. It turned out to be a label on one of the wires that moved out of the way when i turned the case to take out the card, but fell back into place when i stood it back up. Just a suggestion. Good luck.
I've suspected this, but I've peeled off the sticker on my GPU already. From how my rig is setup, it's hard to confuse location of noises:
If my PSU buzzes today, I'll disconnect all my fans just to make sure today.