Symptoms
- Knocking or rattling sound from the pump area
- High-pitched squeal when the trigger is released
- Grinding noise that changes with engine speed
- Noise gets louder over several uses
Likely causes
- CommonPump running dry or low on waterPumps are designed to be cooled and lubricated by the water passing through; running dry causes rapid wear and noise.
- CommonAir in the pump or supply lineTrapped air causes cavitation, which sounds like knocking or rattling.
- PossibleWorn unloader valve causing pressure spikesA malfunctioning valve can cause the pump to strain and squeal when the trigger is released.
- PossibleWorn pump bearings or pistonsAge and hours of use eventually wear internal moving parts, especially if the unit has run dry before.
- Less commonLoose mounting bolts causing vibration noiseA pump or engine that has come loose from its frame can rattle under load.
What to do
- Immediately stop using the machine if you hear grinding or knocking, since continued dry running can ruin the pump.
- Check the water supply is fully connected, turned on, and unrestricted.
- Purge air from the system by disconnecting the wand and running water through briefly before reconnecting.
- Inspect the inlet filter screen for a clog that could be starving the pump of water.
- Check that all pump and engine mounting bolts are tight, since a loose pump can rattle against its frame.
- If squealing happens specifically when releasing the trigger, this points to the unloader valve rather than the pump itself.
- If noise persists with good water flow and no trapped air, the pump likely has internal wear and should be evaluated by a small-engine repair shop before it fails completely.
Tools and parts
- Wrench set
Pressure washer pump repair kitSearch: “pressure washer pump rebuild kit”
When to call a pro
Grinding or knocking that continues after confirming good water flow means internal pump wear; have it inspected before the pump fails completely.
Safety
Use caution
Stop using the machine at the first sign of grinding or knocking; continuing to run a dry or failing pump can cause it to seize and may create a sudden pressure release hazard.