Speaker Hum

Two steps which might help diagnose the problem.

Disconnect the internet/tv cable from the cable box or/and modem.

Try a cheater plug.

In my situation both helped so I purchased a Jensen VRD-1FF IsoMax Digital RF Isolator.  Problem was solved.

Thanks jetter appreciate the feedback I'm going to follow your steps and see how it goes.

Our house was built in the '60s also, and some of the wiring was somewhat upgraded and some was the original 2 blade outlets and it had the glass screw-in fuse box.  One of the best (and actually relatively affordable) upgrades I ever did was to buy a circuit breaker panel at either Lowes or Home Depot (this was about 25 years ago, so some of the detail is a tad foggy) and then I installed some new outlets for my system and then I ran ROMEX down the walls and through my attic to where it could come down and meet the new panel and then I hired an electrician to install the box and hook my new circuits up.

I have read a ton of ongoing & recent threads on this forum and the amps/preamps forum since October, and by scrolling down to October in both forums, I am sure you would come across them.  Everyone seems to agree that a good circuit is a cost effective upgrade; there disagreement on the best way to run the circuit(s). 

https://www.psaudio.com/ps-how/how-to-find-and-fix-hum/

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: