Speaker Hum

@dpop That’s why you are sopposed to add the little labels which no one does and no one reads. 😁

GFCI’s are the only approved way of adding a ground pin outlet where a ground wire does not exist.

Really, any audiophile moving into a home needs to do a thorough inspection. My home was only 15 years old when I moved in and I eventually replaced 100% of the light switches and about 70% of the outlets (so far). All the crap I found. Corroded outlets, loose wires, intermittent switches, wrong outlet types or wrong covers, stuff stuck in outlets, scorch marked outlets and wire terminals.

I’m not going to advocate for cryogenically treated hospital grade outlets, but damn, I sleep a lot better at night by going through the basics thoroughly and getting rid of all the back-stabbed connections. 

Sorry @dpop but all GFCI outlets will work without a ground. It is surge protectors that need.a ground.

Gfci outlets compare the current on the hot and neutrl and trip when they are not equal. Ground not required, but you are required to stick the little "no ground" stickers on.

I would say not likely for a power conditioner to work, and if it did maybe for the wrong reasons.

Given the age of your home, first thing to do is to have an electrician have it fully checked out.  Make sure any 3 prong outlets have a valid ground wire which is properly grounded outside.

You might also consider a good tester like this one: