I found the following for you. As Sarah has said these noises are normal.........
The rumbling or growling sounds of the digestive tract, which scientists call by the very expressive word borborygmi, represent the muscular contractions and expansions of peristalsis, the process that moves the contents of the stomach and intestines onward and downward. Some such noise is normal; its absence when a doctor uses a stethoscope can indicate an intestinal blockage.
The noises are softer or louder depending on the strength and speed of the contractions and on what is in the tract, a variable mix of solids, liquids and gas, both swallowed air and the waste products of intestinal bacteria.
When the stomach is normally full of food and liquid, the noises tend to be muted, but when the contractions are strong, especially when a bubble of gas is moving through the digestive tract or when the stomach is empty of solids, the noise can seem deafening. The contractions are also exaggerated and noisy in some gastrointestinal diseases.