My dog makes a strange popping noise in her sleep. It sounds like an 'plooooooooop' noise, much like that of an exaggerated dripping of water. She only does that in her sleep, every once in a while. Is there a reason she does this? I asked a vet but the vet was baffled and said as long as her airways are fine and she's breathing, to not worry about it. Still... its very loud (far louder than her snoring) and wakes me up at night. She is a Pomeranian btw.