You need to remove and clean the unloader valve. The way this valve works is when you release the trigger the pressure is diverted around the pump through the inlet side so you don't cause damage to the pump. This valve is usually located next to the discharge pipe on the pump where your pressure hose hooks up to. Remove and clean. Be sure to clean port that you remove the valve from also. Use carburetor cleaner. Lubricate the valve with a light coat of lithium grease. This should cure the problem. If not let me know.