Is congestion normal in cats?

The cat is a 12 year old female. She does not have any discharge, does not sneeze, does not sound "wet" when breathing, doesn't have audible breathing at all, and has no symptoms of respiratory infection of any sort. The only thing I sometimes hear are little dry "snuffle" sounds which seem to come from her nose, especially when she is grooming or stretching. I've always heard this in many cats, but sometimes I hear them in her sleep at frequent intervals. In her sleep, she will also give these soft little moans, which are kind of new.. I haven't really heard her do that much until fairly recently. She is otherwise healthy and acting normal. Does anyone else hear this kind of stuff from their cats, is it relatively common? Could it just be from living in a dusty home or something along those lines? It's winter, so the windows are rarely open, and the air is much stuffier and dry.