Took me a few to figure it out, because once it was decased, it wouldn't make any sound at all.
And, weirdly enough, the bodies natural electrical field would make it stop, also. You'd just have to get close to it.
So...narrowed down where the sound was coming from with a paper towel tube. So I didn't have to get close (and shutting off the sound).
Didn't see anything obvious, but as I was sitting there contemplating it, I looked at the plastic sheet which goes under the pcb. The smallest spot on it was discoloured. I put it back over the pcb to see the area on the board which caused it. It was the transformer. One of the pads was floating, but not obvious until closely examined. It looked like a good joint, but wasn't.
Once the old solder was removed and the transformer resoldered, no more noise.