The answer to 'backflow preventer making gurgling noise' is that a gurgling sound coming from a backflow preventer is often a sign of a problem with the device. Backflow preventers are installed to stop contaminated water from flowing back into the main water supply, and a gurgling noise typically indicates that the backflow preventer is not functioning properly.
Some common causes of a gurgling backflow preventer include a blockage in the device, a broken or worn-out internal component, or low water pressure. In some cases, the backflow preventer may need to be adjusted or repaired to stop the gurgling noise and ensure it is working correctly. If the gurgling persists, it's best to call a professional plumber to diagnose and fix the issue.