Humm..
Does he seem in any pain or discomfort?
Are you nursing or formula? If formula, what kind, if nursing, are you eliminating anything from your diet?
Tummy rumbling sounds like LOTS of gas. My lo's used to do that, but he would also scream and cry in so much pain.
Have you ever had an upset stomach and your tummy was cramping, and gassy, and you feel all the gas bubbles in there. That is what is sounds like to me.
With us, my son could not handle milk or soy. Could just be lactose, but more than likely could be milk or soy and that could also be causing his reflux.
Let me know about the questions and I can help you a little more.
Wendy