So what’s the verdict? Have you found the source of the hum?
I still haven’t located the source but I’m going to assume its the doorbell transformer. If/when we remodel the kitchen and upgrade the electrical system, finding and replacing that transformer (and relocating it to somewhere accessible) will be on the list.
I’ve talked to my skinny nephew about helping me replace the two OG bathroom exhaust fans. If he does so I’ll ask him to look around and see if he can spot the transformer while he’s up in the attic.
Did you disconnect the wires you see? I had this exact problem years ago and just stood on a chair and disconnected the wires in the box and problem solved. So far the house hasn’t burnt down.