I seriously doubt this has anything to do with your problem, but my Rio 600 was spitting out air every once in a while and I couldn't determine the cause, and then I realized that nitrogen bubbles from my sand bed would catch on it on the way to the surface and eventually get sucked into the intake. The noise made me think it was broken or something, but eventually I saw it happen.
92-gallon corner tank, 100lbs of LR
, 140lbs of sand, 250watt 10,000K MH
, 110watts of actinic PCs, Mag 7 return, custom refugium, AquaC EV180 w/ Mag 5
Female lyretail anthias, eyelash blenny, tomato clown, saddleback clown, firefish goby, 2 sand-sifting stars