Knuckle cracking noise coming from belly!?

Vane
Has anyone heard a sort of knuckle cracking noise coming from their belly!? And it's not my ribs cracking, I hear it sometimes when baby sticks out her butt! My midwife almost didn't believe me, but now my husband and sister have hear it too! The Internet seems to think it may be popping of bubbles in the amniotic fluid.