system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What's actually happening when my stomach is 'rumbling'?

I'm fasting for a capsule endoscopy and my guts are going off.
gpt
Because there's not much solid material in your intestines, it's basically gas and liquid getting pushed around when they move (which they do regularly, to mix your food and to move it 'down the path'). 

You're hearing the gas/liquid gurgling through digestive tract as this occurs, which is louder than squeezing and squishing the semi-solid mass if you had food in its place.