What causes your stomach to growl when you are hungry?

When you are hungry, your stomach and small intestine produce growling sounds called borborygmi. This happens because your digestive system continues to contract and move even when there is no food present. The brain sends signals through the vagus nerve to keep the digestive muscles moving in a process called the migrating motor complex, which sweeps through the stomach and intestines roughly every 90 minutes to clear out remaining food, mucus, and bacteria. These muscle contractions push air and fluid through the digestive tract, and the movement of gas and liquid through the hollow tubes creates the rumbling or growling sounds you hear. The sounds are actually louder when your stomach is empty because there is no food to muffle them.