Vibration in the uterus

Katie | 👼🏻👼🏻👼🏻🤰🏻

I am at the end of my 12 week, and I noticed my uterus area has been vibrating/rumbling (that last around 2- 3 secs each time)very regularly, mostly when I’m lying down or sitting down. I know it is not my tummy or gas because it feels much lower and it happens when I’m hungry and full. I thought it’s too early to feel the baby and even so, how is it possible for the bb to make that much movement? Anyone know what it is?