[FONT="]I have a pre 1999 nautilus fns 48 de filter. Recently there has been a consistent gurgling noise coming from the top of the filter housing which seeems to be coming from the air relief pressure valve system. No water is escaping from it and I sprayed shaving foam around area but didn’t see anything.Pressure reading is at 20 lbs which is normal but seems to be jumpoing around a little bit. Everything else in filter system seems to be fine no air in strainer housing,good prime and minimal air bubbles from return jets. Any thoughts on cause and how to correct. Thanks[/FONT]