If it makes noise w/o feeding CO2 into it, there's something wrong with it. Open it up and make sure the impeller is seated correctly and that nothing has been sucked in there.

I used a Rio 50 powerhead (the smallest I could find) and an Azoo diffuser with good results. I placed the input screen of the power head right on top of the diffuser disc so it looked like one unit. The power head shaded the disc so algae wouldn't form on it.

-Russ