system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What causes your stomach to make audible 'grumbling' noises when you're hungry.

The 'grumbling' noises that your stomach makes when you're hungry are sometimes louder than others. What causes it to be so loud that it can be heard by others?
gpt
Your tummy and digestive tract as a whole use muscles  and sphincters (Valve like muscles) that contract slowly to move large masses and gas. When full, the release of gas within the tract by valves create a grumbling noise that is muffled by masses of food. When hungry, the movement and pressure release of gas isn't muffles by anything, allowing the noise to be more noticeable.