Thanks for the replies.
I'm in Australia by the way... so my outlet is constantly delivering 246-248V. So that all seems fine.
The hum is audible through the speaker cone. There is a buzz along with the hum also. Putting my finger on the cone eliminates some of the hum. Sometimes just grabbing the cable eliminates the hum.
I can also hear some radio through the speaker.
Trying to vomit out as much info here....
No conditioner to try out.
There's obviously some kind of interference, but I'm dying to know why it is happening. And why it disappears when I just lift the cable slightly...
Should I be looking at getting a shielded IEC power cord?