What causes water pipes to whistle?

The whistling sound from pipes is mainly a result of turbulent airflow within the line due to constriction in the line or a partially closed or faulty air release/pressure-releasing valve.

There could be obstructions inside the pipe's interior or a build-up of sediment deposits along its walls making the area too narrow for smooth and uniform water flow.

When high water pressure forces its way through such narrow openings inside a pipe it gives you whistling or squealing as well as rumbling sounds with some associated vibrations from the pipes.