Well I can think of a few bacteria that do not need to breathe. In all respects everything which makes a xenomorph is actually biologically feasible. Definitely not possible via natural evolution on our planet, but feasible.
Actually Aliens make sounds to communicate. Based on what I have witnessed in the films, I believe that all aliens share a very basic mental link, which can only communicate more base emotions, with the queen's being the most dominating and powerful of them all. In order to communicate, xenomorphs need to vocalize. This is the only logical explanation to why they generate sounds, let alone on such a broad range. However, because they do not breathe, it is most likely that they actually only take the basic structure of an organism's lung, and while it partakes in no respiratory function and is not linked to a circulatory system, it allows for the flow of air for communication.
"If anything in this life is certain, if history has taught us anything, it is that you can kill anyone." - Michael Corleone