The answer to 'why is my backflow preventer making gurgling noise' is that a gurgling sound from a backflow preventer is often a sign of a blockage or air in the system. This can be caused by debris, mineral buildup, or a problem with the internal components of the backflow preventer. The gurgling noise indicates that water is not flowing through the device properly.
To troubleshoot this issue, you'll want to first check the backflow preventer for any visible debris or blockages. You can also try flushing the system by turning off the water supply, opening a faucet downstream, and then turning the water back on. If the gurgling persists, you may need to have a professional plumber inspect and clean or repair the backflow preventer.