said by NetFixer:I don't know. The house wiring is all CAT6 and as part of trying to fix this noise issue I actually did replace all of the terminations, so pretty sure everything is properly wired.
It sounds as if your home telephone wiring is either not twisted pair, or you have it accidentally wired with split pairs, or there was a short between one wire on two circuits, or possibly a short to ground on one wire. Balanced twisted pair wiring should have canceled out any noise between circuits, or any external noise.
However, the cleaner power supply seems to have fixed your symptom (and it may have been cheaper than fixing the wiring).