There was a problem with just the few airports in the world that are below sea level, but other than that, there's no reason why you wouldn't hear any sound in most airport except one.
Instead, it might be an issue that depends on the airplane used, some are making lots of noise when seen from the outside, even when everything is turned off.
Try the default A321, which is quiet when engines are off. The default 747, for example, makes lots of noise even with engines off, and that makes more difficult to hear GSX sounds.