Odd "squirting" sound from water pump
So I'm starting a new 55 gallon saltwater tank and have a Mag-Drive 9.5 pump set up in my sump. Pump is working great but it randomly makes a "squirting" or "bubble" noise. I can see NO bubbles making it through the bubble trap because the water level is higher than the ledge (no waterfall effect). It is also NOT the pump rattling against the walls and bottom of the tank (silicone mat solved that).
So what could this be? If it were constant, I would suspect a trapped air bubble inside the pump but it's infuriatingly random but frequent enough to keep me awake. There is NOTHING else in the tank but saltwater.
Any help would be appreciated! Thanks!