One of my older dog's (12 years old) stomach sometimes makes a gurgling kind of sound. When I hear it, it's at night, if that makes a difference. It's not like a stomach grumbling, but like bubbles. It sounds like his stomach is gurgling. It's loud enough that I can hear it from a couple of feet away. He has done this for as long as I can remember, but I was wondering what it was. Does anyone know?