I've been riding out current events at my sister's home.
Recently we had a very strong storm that knocked out the power for half the day.
Before the storm the ZMA hummed and I could hear a hum from the speakers. I'm also running a 230v ZMA on 115v power so there is a step up transformer. That also buzzed very loudly.
After the storm the system is dead silent. I'm guessing what ever they replaced to get the power back on was going bad.
All this brings me to maybe you want to try a regenerator. At my place which has terrible power quality. I run a PS Audio SP3. It powers Torii MKIV, PS Audio DSD, Teddy Pardo power supply (for small DC stuff)
I do want to upgrade to a P12 not only do people report that it gives even more improvement in sound it also delivers a lot more power.
If you do want to give one a try I suggest calling them and seeing if they can work a deal with you.
Even if you didn't have a hum I would suggest a regenerator for the SQ improvement.
Decware also makes an isolation transformer. I've not used it so cannot comment of the efficacy if it.
https://www.decware.com/newsite/ZLC.html