Cavitation, eh ? I'm familiar with that concept as we have jet skis. THeir wear rings when worn and the intake comming 'unhooked' from the water, cause that issue with their pumps.

Why would this just now show up-- after 3+ yrs of operation ? I dont see any air getting into the pump strainer. The pressure on the filter remains the same as in prior years.

Downsizing the pump/motor--

Reduce it to 1.5hp ? Would this cause other issues with the filter/piping as it was designed ( I assume...) to use the 2hp pump ?