I believe the issue is that the factory o-ring material deteriorates, leaving gaps that allow air into the system. I am not aware of a screen.
The oring can stay in the pump. Use an oring pick to check. Otherwise you now know why air is leaking into PS fluid.I removed the hose to the inlet on the power steering pump and there wasn't a ring at all. I did the same thing to an 05 accord before and there was a ring.
Anyone else not see an o-ring on the return hose of the power steering pump? The noise seems to be gone but it hasn't been cold out.