If all else fails an AC regenerator is the answer, but expensive. As mentioned, probably better (and cheaper} to solve the problem at the source with an electrician, but a regenerator does improve the sound even where no hum existed.
AC hum
Had a Mini split ac unit installed, because a new line was installed in the panel I had to have a full home surge protector installed at the box( now code). Now I have ac hum through the speakers in both of my systems. Other than having the house re-grounded, is there any device I can plug into the wall socket to get rid of the noise? Any assistance would be appreciated.