However, POTS is degrading too. I put up with a constant hum on the lines> at home, especially during the wet seasons like Spring.
Most of the time the remote person doesn't here it, but I do.

Most POTS in existance now would be nearing the end of its operational life. One of the problems it sounds like you're hearing is water + DC voltage = constant corossion, those copper wires are slowly decomposing out there in
the water.

I suspect we ended up with Copper to the home here on the end of fibre for our NBN, is that, this copper is the newest. The exchange links would be the oldest and thats what they won't want to replace.

Thought and Speculation,
Spec

--- SuperBBS v1.17-3 (Eval)
* Origin: Scrawled in haste at The Lower Planes (21:3/101)