just bought a home with a 18K pool. Previous experience has only been with SWG pool. In addition to fighting algea, my Hayward multiport valve makes a cavitation noise when on Filter setting. Reducing flow does not work, and I have verified no leaks on pump suction. The noise goes away when I change to backwash, waste, recirculate, or rinse settings. I tried installing a ball valve at the pressure gauge to bleed out air, but no luck. Pressure downstream of the sand filter runs about 18# and I have verified good return flow. Any advice on what to try next?