There is no air bleed on that filter. It's a smaller version of my S-244T. If you look at the manual, the center pipe from the laterals is a loose fit to the valve assembly and that's where any trapped air would escape. Sounds like you may just have a low water level and are sucking air from the skimmer on a cyclic basis. For now I'd just try raising the water level an inch or so and see if the situation changes. With good flow the trapped air in the pump strainer basket should purge itself.
Al