It seems to be happening more often. It doesn't matter if it is the bath, shower, toilet flushing or washer. Where do I begin my quest to fix this?

I had a similar hum, tracked it to an outside spigot with a garden hose attached. The spigot was open but the sprayer on the end of the hose was closed (no water was running out of the hose). The outside spigot has a anti-siphon (vacuum breaker) valve in it that would hum when any water was running elsewhere in the house. The humming stopped when the handle on the spigot was closed.