I have an Eheim Ecco 2234 (one of 7 Eheims I own), and it's recently started making a whoooshing sound. Basically, it sounds like it is blowing tiny air bubbles into the water, but I can't say I really see any air. It fluctuates as to how loud it is, but it is more or less consistently making the air bubble noise. I tried cleaning it out (only been 3 months, normally they go about 6), but it actually seems like it may be louder now. The other 2 Ecco's I have run silently, and this one has for almost a year, but now is making this sound. Any advice?