It could be any number of things. The singing is the result of a high velocity water flow and turbulence.
This can be caused by high pressure if you measure your water pressure and it is above 80 psi a Pressure Reducing Valve should be installed.
there is a restriction somewhere in the path of the moving water. This could be a partially closed valve, debris in an aerator, a piece of a broken faucet washer blocking a stop valve, or, any number of things.