This usually points to an air leak or restriction on the suction side of the water pump. Common causes include a loose inlet fitting, cracked hose, clogged strainer, or a failing pump check valve. Also confirm the fresh water tank has adequate water and the tank vent isn’t blocked. Tightening connections and cleaning or replacing the pump strainer often resolves this. Issues like this are fairly common in RV systems, and resources and guidance from RV-focused brands like Popular RV can be helpful when troubleshooting.