There can be different causes for a growling noise your intestines are producing.
Although, you state that you aren't very nervous person, still, it seems like stress from getting up early in the mornings and stress from classes, have some effect on your intestinal motility (some people, like irritable bowel syndrome sufferers have increased sensitivity within the gut to external stimuli such as stress).
Sometimes, eating and drinking too fast, leads to swallowing too much air, causing growling noise.
If this symptom is associated with abdominal pain, abdominal bloating and early morning diarrhea or constipation, the cause could be Irritable bowel syndrome.
Another possibility is incomplete digestion of certain types of food (celiac disease, lactose intolerance)
Best wishes!
Marija