Hayward filter air sound

[Poconos]

A couple things I found about this filter...same or similar to mine, an S-244T. If you do get air rattling around in the valve assembly it will persist if the flow isn't high enough to drive it out. This happens to me when I vacuum sometimes, and the vacuum hose restricts the flow on the suction side. Going back to full skimmer flow corrects the problem after a few minutes. Every time I vacuum I get air in the system because I don't fill the hose with water before hooking it to the skimmer. Too much bother. Next, whether it is by design or just the way it happened, the center pipe in the filter is a very loose fit to the mating pipe in the valve assembly. This center pipe is the water return from the laterals at the bottom of the filter. With the loose fit any air that gets into the top of the filter, above the sand, is at a slightly higher pressure than the water in the center pipe and the trapped air will leak past the sand, through this loose joint, and get purged from the system.
Al
Another thought...what pressure is this filter running at? Reason I ask is possibly your flow is being reduce by the eyeballs in the return jets or any other devices you have in the return path. I bored out my eyeballs to cut the flow resistance and up the flow a little. Not because of the air issue but just because I hate things that restrict flow.