I have a new Waterway Cartridge filter with my new pool. It has been working fine for the last few weeks. Now I have a bad humming noise coming from the filter. Almost like a vibration. It is definitely not from the Hayward pump. When the timer kicks off, it does not start right away, but soon after the noise begins. I cleaned the cartridge, just in case. The psi is at the right amount under 10. There is proper pressure coming from the inputs into the pool. When I switch the value to only go to one or the other input into the pool it stops for a few minutes then starts again. There are not real working parts on the filter. Can it be the O-Ring that seals the filter cover? There is no leak of water, which I had already but was repaired with an O-Ring change. I am a little perplexed. The filter does have a psi gauge on the top and a screw pressure release to let pressure off when opening the filter for service. I don't feel it is coming from either of these, but I could be wrong. An ideas?