Diagnosing and fixing transformer hum

The house was built in 1941. Even light fittings seem to hum.

Its really hard to find explanations of DC offset that don't make my eyes blur and head ache. Briefly it can be any fault in the electrical system- any connection from the panel to the light or appliance running on the circuit. A home wired in 1941 has had 70 years to develop faults.

The easy fix would be a hum buster. Granted you already tried one so a bit of a long shot but worth it compared to the alternative. Which is starting at the panel to take everything apart and clean and improve mechanically (I'm talking like emery or sand paper wire ends, bus bars, etc) and/or treat the whole thing with TC. Then continue on to do this for every wire and replacing every outlet and switch throughout the house.

The wire is fine its the connections that oxidize and cause trouble. Can't guarantee this will totally eliminate your DC offset hum but it will for sure have your system sounding a whole lot better. 

btw if that sounds like a lot, I took my panel apart all the way down to the bare bus bars. Those little brackets that screw into the copper bus bars? The ones the breakers clip onto? I removed all those, cleaned, and treated with TC. If I can do it you can too.

@tuberist 

Good thought. The DC blocker also includes a tester, thanks. A couple of outlets are wired incorrectly, but hum is there when using the outlets with no problems. I will get an electrician in to do further checks and fix such issues, for safety if nothing else. 

NoRom and 3EP: 

yes, I was thinking that maybe the house move loosened things. Unfortunately, the way the unit is designed, it looks like getting to the mounting bolts of the transformers means removing the circuit boards underneath, which I don’t have the tools for. The dealer is in a different state, and we’re on lockdown. So I will count myself lucky for having luxurious problems and wait a while to have it checked out. 

Miller 

I will get someone in to do some safety checks and tend to a few issues I can already observe. A local dealer has recommended his electrician as being audiophile sympathetic. When he’s there (and confirmed nothing is live!) I’ll polish connections like you suggest. Even though switching off all the other circuits didn’t fix the transformer hum, it did lower the hum at the speakers, which suggests some combination of ground loops, EMI, etc. So yes, point taken.

BTW, what do you mean by TC? I presume not “tender care”? 
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