I just wanted to reiterate what WinterWish said earlier... that is it just a hungry tummy rumble, makes him uncomfortable, he goes outside, eats grass, feels worse... and on and on.
Mine get grumbly tummies sometimes late at night, and a half a piece of bread always settles them down. Is he interested in food at 4am? Might a little snack help?
So sorry for all the worries in your household!