RESTRICTED INLET OR 
AIR ENTERING INLET

Check inlet screen/filter
Clean or replace if needed.

If air enters your system, upstream from the pump, serious pump damage can occur.  A tell-tale sign is pump chattering.  You can also hear pressurized air coming out of the nozzle.  

Air can enter the inlet through a loose connection if your pump is trying to draw more water than the water supply can produce.  Make sure you have an adequate water supply  A loose connection on your fittings or inlet quick connectors may appear as a leak when the pump is not running but can turn into an air injector when you pull the trigger. If your inlet connections are loose and leak, when the pump is running, this means your inlet supply is greater than the needs of the pump.  This is a good condition but you should still fix the leaks.

Air can also enter through low pressure soap injectors or high pressure soap injectors. 

Low pressure injectors, if working properly, will not suck air at high pressure.  They will suck air if the wand has a soap nozzle on it and the pickup tube is not in a container with liquid in it.  Regardless, this is never a problem for your pump as the air is being picked up after the pump.

High pressure soap injectors however will pick up air, before the pump, and send it through your pump and hoses at high pressure.  These devices are located before the pump.  If you have a loose connection or the pickup hose is not submerged air will be sucked into the pump - this is not good at all.  

If your pump cavitates, for an extended period of time you will soon need a new one! When working a distance away from the machine make sure someone is checking the soap level.  

All inlet air leaks should be attended to right away or the pump will cavitate and eventually destroy itself.