concentrators/generators that use pressure swing adsorption technology should breathe. That means that if there is 2 sieve beds, it should breathe...as the valves switch the compressed air from one sieve bed to the other. Only units I am aware of that you wont hear breathe are the Sequal units, because they have a totally different sieve bed design with a rotating motor on the bottom of it that constantly cycles the air through the parts of the sieve bed, eliminating the breathing noise.
And believe it or not, your generator probably has a holding tank (product tank) of some sort in it, but its probably small...not a 30 gallon tank like you may be thinking of
