Non return valves often whistle and hum. Particularly if something is partially obstructing them or getting in the water flow.
They can be serviced - all they often are is a spring retainer and a ball or flap. Usually one end can be opened for disassembly.
Another option is to mechanically isolate the valve from the house using a flexible quick connect or similar that won't propogate the resonance through the pipework.
People don't ever seem to realise that doing what's right is no guarantee against misfortune