[LunarBerry]

hmm if it sounds almost like an asthma thing, it my be a reverse sneeze, or in some cases, like mine, she has allergies and a small nasal passage, which makes her snort/honk like a duck or pig when both awake and sleeping... thus I call her my little pig/duck XD but either way, those are the lesser worrisome conditions and are harmless for the most part.
Other cases might be a condition of collapsed trachea at worse or they just have a cold/cough/irritated throat. When in doubt, have a vet check them to be sure.