I have tinnitus and it sounds just like power supplies, except it comes from nowhere.
So, when. I hear the squeal, I turn my head. If the squeal noise follows the movement of my head, tinnitus. If it stays put, power supply!
It's like skunk and pot! (I'm in Canada, it's legal and everywhere.) If I smell it, I look around. If I see a burrow, skunk! If I see a dozy looking dude with red eyes...