Age old problem.......humming pipes

[Schraderpl]

Brand new PRV. Brand new toilets. The humming at night is driving me crazy. I shut off all incoming water to the house and turn on a faucet to drain the lines and it still hums. I thought I solved it tonight by turning off the water at the meter and draining all water out of the line. Sweet bliss. It was quiet. Within an hour the humming was back. I am sleeping with ear plugs.