what causes a stomach to rumble?

Question

besides being hungry?

Answer 1

motion known as peristaltic action makes the gas in the stomach move around, and you hear it as a rumble.

Answer 2

Hunger.
Irritable Bowel Syndrome also cause noises in the abdomen.
Borborygmus (plural borborygmi) (from Greek βορβορυγμός) is the rumbling sound produced by the movement of gas through the intestines of animals or humans. The word borborygmus is an onomatopoeia for this rumbling.

The "rumble" or "growl" sometimes heard from the stomach is a normal part of digestion. It originates in the stomach or upper part of the small intestine as muscles contract to move food and digestive juices down the gastrointestinal tract and functions as a sort of intestinal "housecleaning".

Although this muscle contraction happens whether or not food is present, rumbles are more common after the animal has gone several hours without eating. This may be why a "growling" stomach is often associated with hunger.

Rumbles may also occur when there is incomplete digestion of food that can lead to excess gas in the intestine. In humans this can be due to incomplete digestion of carbohydrate-containing foods including milk and other dairy products (lactose intolerance or the use of α-glucosidase inhibitors by diabetics), gluten (protein in wheat, barley, and rye) (celiac disease), fruits, vegetables, beans, legumes, and high-fiber whole grains.

Answer 3

hunger
or
gas