Do you mean the hum is coming from the components or from the speakers? If it is from the components just unplug each one at a time and see if it goes away,if it does then you will know which one is the trouble.
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You could have a feedback issue from your main panel. Turn the breaker off that is above and below the one you are using for your system. If this stops the hum then turn one of the breakers back on and check again. If the hum comes back then find what the breaker is supporting and work from there.
I am no pro at this by any means but I have experienced these issues before. I have also run into reverse polarity issues.
disconnect each component separately and ascertain if the hum still exists to determine which unit is causing what is most likely a "ground loop"---or use a cheater plug on each unit and see if it takes away the ground loop--but cheater plugs as a permanent solution is never a good idea since it floats away the ground. Sometimes using shielded interconnects or balanced ones can help as well.Theres alot written on solving ground loops on the internet---