AC hum

I would not attempt to solve this with a new device. As @skids wrote, I’d ask your electrician to check things. Not only could it be something as simple/stupid as wiring getting moved, but there might have been something new that needs to be fixed in the panel, or the house service, like a loose neutral in the panel, etc.

Also, congrats on the whole house protector. :)

One  thing to test is to turn the breaker to your new heat pump off and see if that affects the hum.  If it does not, chances are something else got moved, possibly accidentally.  For instance, your neutral to your stereo might have been loose before and the electrician could have just nudged it. So, really, don't try to solve this as an audiophile issue.  Solve it as a potentially bad electrical issue.

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.

Puritan 

Puritan PSM156  

Ground Master City

Route Master

Worst comes to worst 

you run new ground rods and install a Ground Master connected to those ground rod/s