Diagnosis
This is cavitation—the pump is trying to move more water than it’s receiving, creating vapor bubbles that implode. It’s damaging.
How to Fix It
Immediately check your water supply. Ensure the faucet is fully open, the hose is 3/4" diameter and not kinked, and the inlet filter screen is clean. Use the widest spray tip (40° white) to reduce demand.
If That Didn't Work
You may have a restriction in the high-pressure side. Check for a kinked high-pressure hose or a partially clogged spray tip. Soak the tip in vinegar to dissolve mineral deposits.
Heads Up
Prolonged cavitation destroys pump pistons and seals. If the noise persists with a perfect water supply, the pump’s internal check valves may be stuck or damaged.