City water inlet connection has an internal check valve....when they are failing they will start humming. Replace.
And could be water pressure regulator......crud built up on valve/seat area.
If yours is rebuildable just disassemble and clean out internals. Otherwise...replace.
Also can get a humming sound from water heater outlet (check valve) when it is failing. Replace
ON EDIT:
Noticed you have 'Yuma' listed as location.
Very hard water....you have crud built up
If you are going to be in Yuma area much (or Southwest US) might want to invest in a portable water softener......several brands (On-The-Go, FloPur, Water Stick)
They will stop that build up...check valves, faucets, toilet water valve, Water Heater etc.
