After purchasing one of these for a 30 g Qt and returning a defective one, the replacement is working fine. The motor was surging very bad on the first one and it was putting tons of bubbles into the tank. We returned it and got another, and it seems to be working perfectly. You might have got a bad unit. The motor should not make hardly any noise, the air adjuster is probably installed backwards (both of ours were), and you can put a sponge behind the filter part to cut down on bubbles. The manufacturer's quality standards are somewhat lacking, but we got lucky on the second try. Had to swipe a part from the first unit though, because they forgot one in the second box. Good luck.