I believe it's the stomach muscles clenching and dispersing stomach gases around your guts. But I'm not certain.
Hello, if you are really hungry it fells like there's something moving. So the muscle thing might be true. As an analogue I thought about a funnel with a connected hose. If it runs empty it makes some sounds. But the sound is supposed to stop if the hose is completely empty. Does stomach growling stop? I don't know. Regards Gyro
Maybe you could conduct an experiment to find out Gyro... https://www.youtube.com/watch?v=KSEMqWptAmM