Riddle Me This Batman; Low Frequency Hum: SOLVED

Shut down all electric.. UNPLUG from park power.. Suspects include the Automatic Transfer switch (if you have one) and converter and any other power supplies. Cell phone chargers and the like that contain Transformers or coils.

Also what "note" is the hum... if you can do it listen to 60 cycles. That is between Bb and B or A# and B take your pick. A couple 3 octaves to the left of center.