I recently noticed that when I switch the flow of water from 100% to the in pool returns, to 100% to the waterfalls, the pressure reading on my Hayward DE4820 filter jumps from about 18PSI to almost 28PSI. Attaching a video. Any idea what might cause this? Do you hear that noise before I switch the valve? I think it comes from the mutliport valve. Sounds like sand bouncing around in there, but I'm guessing it's actually air?
Also, in case it's related, I've noticed lately that when I turn the pump off, there's a surge of pressure that forces water to squeeze out from the lid of pump strainer. The gasket on the lid is a Hayward part, is well lubed, and was recently replaced.