If the nozzle has even a speck of dirt in the tip, it may cause enough of an obstruction to cause the unit to pulsate. Use your nozzle cleaning kit to clean tip. If there is air in the hose it may also cause pulsating. Purge air from the hose by pulling the trigger and allowing the water to flow. If this does not cure the issue please contact us, and a service representative will be glad to help.