I have an aqua culture for a 30 gallon which has two air tubes which is ultra quiet--I can barely hear it when I'm right next to it
my aqua culture for my little ten gallon is relatively noisy---I can hear it going if I'm in the same room
And absolutely positively do not get an AirTech---when I had it set up I could hear it 2 rooms away
the bigger the less noisy they are which is a big factor for me.
That's all the knowledge I have to share