i got the M size. When co2 is off , the reactor is very silent. but when its on , there will be some splashing sound like TS said . but its not a problem to me . Mine doesn't come with hose clamp , but i added it to play safe incase it leaks.
Take note , the hose adaptor , has 2 end. 1 end is smaller and the other end is bigger. The bigger end should be connected to the hose while the smaller end connected to the reactor . So far , i find this is the best diffusion method for me =]