The answer to 'backflow preventer making noise' is that a noisy backflow preventer is usually caused by a problem with the internal components or water pressure issues. Common symptoms include a loud hissing, whistling, or vibrating sound coming from the backflow preventer. This can be caused by a worn-out or stuck check valve, a buildup of sediment, or excessive water pressure.
If the backflow preventer is making noise, the first step is to check the water pressure. High water pressure can cause the backflow preventer to make noise. You can install a water pressure regulator to lower the pressure. If the pressure is normal, you may need to disassemble and inspect the backflow preventer. This is usually a job for a professional plumber, as backflow preventers have complex internal mechanisms that require specialized knowledge and tools to service properly.