OK I took off the panel and listened/felt for the hum...it was very hard to pinpoint.
Here is a picture of what I'm working with:
If I touch anywhere on that silver "box" (that the circuit board is mounted to) or the circuit board, I can feel the hum. Also on either of the 2 other components mounted on the "box." It doesn't really stand out on one component more than another...and unfortunately I'm not sure what to look for.
Hopefully the picture could help you tell me what to look for / inspect?