It's probably the regulator. These things can oscillate, in combination with the valve, often slowly enough up and down, that they call it "hunting." More pressure is usually the cure, but now that they have the fixed-pressure Accu-Sync, adjusting the pressure isn't an option, and other than trying a new diaphragm in the valve, assuming it's an older valve, there isn't any easy answer other than ditching the Accu-Sync in favor of a stand-alone pressure regulator.