This is from a post williewonka made. Hope this is okay.
turns out - all that was required is a slight "repositioning" to a couple of the wires in the breaker panel.
- the electrician had repositioned a couple of breakers and those live wires ran parallel to (and was touching) the neutral wire of the cable run for my dedicated audio outlet
- He just moved the wires to put a little more space between them
- the hum disappeared.
Regards - Steve