I've never really wondered about why my stomach growls, at least not to the point where I went out to research it, but this entry from Indiana Public Media's Moment of Science explains a lot about what is going on when my stomach generates what Winnie the Pooh called a rumbly in my tumbly.
When the GI tract has finished digesting a meal, it continues to process the liquids and gasses remaining in the intestines. This process often causes your stomach to rumble when you’re hungry. Stomach growling is caused by intestinal contractions squeezing and popping intestinal gasses. Actually, stomach rumbles are simply flatulence that stays inside the body.
The same contractions that cause your stomach to growl also clean out the GI tract. To see how this cleaning movement works, picture a long hose made of a pliable material. If there were an object, say an egg, at one end of the hose, you could push it from that end to the other by squeezing all along the length of the hose.
hattip to Boing Boing