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.