The Tetra Whisper brand gets some good reviews. A friend had one and she came home from work and it was very noisy. She ended up having a bad motor and returned it to the store. Her replacement one is perfect, the only thing you can hear is the bubbles coming out of the stone. Seems like they are hit or miss as far as quality is concerned but they are fairly reasonably priced. They have different sizes for different tanks so pick the one that is the best match for your tank.