The answer to 'why is my zone control system making loud noise' is that the system's components, such as dampers, motors, or fans, may be malfunctioning and causing the noise. Common causes include worn bearings, loose parts, or issues with the system's wiring or controls.
The noise could also be caused by airflow problems, with the system working harder to maintain the desired temperature and pressure in each zone. This can lead to increased vibration and noise. If the noise is accompanied by uneven heating or cooling, it's likely a sign of a more serious problem with the zone control system.