An empty tube, squeezing anyway
Why Does Your Stomach Rumble?
Your stomach does not stop working when it is empty — it sweeps itself out, and an empty tube is loud.
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Step 1 of 5
Your gut never stops squeezing.
Rings of muscle travel down the tube whether there is food in it or not. With a meal inside, that is quiet. Empty, it is not.
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Step 2 of 5
Empty means air, juice, and lots of room.
Sound needs space to resonate in. Food damps everything; an empty stomach is a chamber of gas and liquid being sloshed about, and it carries.
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Step 3 of 5
Every couple of hours it does a proper sweep.
When nothing has arrived for a while, a strong wave runs from the stomach right through the small intestine, clearing out leftovers and bacteria.
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Step 4 of 5
Hunger itself is a chemical, not an empty feeling.
A hormone builds up when your stomach has been empty, and it peaks near the times you usually eat. That is why hunger arrives on schedule, not on volume.
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Step 5 of 5
Which is why hunger comes in waves.
Miss a meal and the feeling builds, then fades, then returns. The level rises and falls; it does not simply climb until you eat.
Rumbles are louder when you are hungry but they happen after meals too — you just cannot hear them through the food.
The short version
A rumble is your empty gut sweeping itself out with nothing inside to muffle the noise, and hunger is a hormone that peaks on a schedule.
Try it yourself
Press an ear to a friend's stomach an hour after they last ate. The gurgling is there whether or not it is loud enough to hear across a room.