Sometimes the hum is caused by a light dimmer. The dimmer works by chopping off AC cycles and this generates a lot of electrical noise. Torroidal (donut shaped) transformers are especially susceptible to this. When the light in my range hood is on the dim setting, the balanced transformer in my power conditioner buzzes.
Amplifier Transformer Hum
If you narrow the hum down to the amplifier's transformer, try to determine which circuit the amplifier is running off of. Then check the circuit breakers in the service panel.
Chances are that your amps' circuit is on the opposing phase of some or all of your other audio circuits and therefore generating some AC noise thats affecting the transformer.
Have an electrician move all of your audio circuit breakers in the service panel to the same phase of 115 volts.
Just for grins I moved my amp's circuit over to the opposing phase where my other dedicated audio circuits are to see what sonic improvements I may find. No sonic improvements that I could tell but it cured my transformer hum and the transformer has been almost dead silent every since.
Chances are that your amps' circuit is on the opposing phase of some or all of your other audio circuits and therefore generating some AC noise thats affecting the transformer.
Have an electrician move all of your audio circuit breakers in the service panel to the same phase of 115 volts.
Just for grins I moved my amp's circuit over to the opposing phase where my other dedicated audio circuits are to see what sonic improvements I may find. No sonic improvements that I could tell but it cured my transformer hum and the transformer has been almost dead silent every since.