I got the X5 on my 55 gal tank in my bedroom (where I sleep). :) It's very quiet - just as quiet as my Rena. I do have it setting on carpet, and make sure it's not touching the aquarium stand or the wall at all. (this does make a difference in the vibration noise). The only thing I don't lie about it is I had to jerry-rig a closure for the second outlet because they have no valve to shut off the second outlet - and I only need a single outlet, but wante the power of the X5.
Bottom Line: It's not a Rena, but it's much cheaper, and very quiet, and it circulates air - what more do u need from an air pump? :)