It is digestion in progress. Your stomach muscles are contracting, swishing up your food and moving it along into your intestines for further processing. It can be a noisy process!
There could be several causes for this, none of which is anything particularly troubling. The most likely possibility is that you have a some indigestion. Other possibilities include gas and over-eating.
The stomach contains acids that sometimes rumble and gurgle whether a person is hungry or not. The digestive system is usually in some mode of digestion or evacuation.
