Indeed, the AquaClears are very quiet...so are the Aqueons, but a bit more noisy as compared to the AquaClears because of their final stage with water coming through the "bio bar" for oxygenation and polishing...though not annoyingly so...
In my setup, I have a unique situation in that bubbles from my two 18" bars are causing the AquaClear 110 to suck them in, creating a NASTY "box of rocks" noise from the filter because of the grinding the motor is doing to the bubbles, thus causing microbubbles and it's REALLY annoying...
This is the price I pay for keeping the bars, though, and right under the intake -- even though I have been told this is going to eventually burn out my rotors and motors...
I've been trying to figure out why my aqueon started doing this after adding the bubble bar, getting the micro bubbles too. Good to know!