You feel hungry when your stomach is empty.

Hunger is registered in hypothalamus, a part of your brain. Many body functions including hunger and feeling full are regulated by hypothalamus. When you eat the food is digested and moves to the intestine. The stomach becomes empty again. This is the reason why you become hungry.

What is the reason for tummy rumble? To digest the food your stomach and intestines are always moving. When the stomach is empty it is filled with air. The air is pushed around in the stomach and intestines and this causes all the noises.