What Causes Loud Random Noises From The Stomach?

My husband is a healthy 45 year old. He is pretty active. The last 2 months his stomach has been making obnoxiously loud noises. They are not hunger pains. He has no gas or problems going to the bathroom. He has no pain. Whenever he sits down or lies down, the noises begin. I can t get over the loudness of them. It is really bothersome to both of us. He went to the Dr., had some blood work. They want to recheck his thyroid in another 4 months. Can that be the problem? He didn t get an answer today but has an appt. with a gastroenterologist next week. What could it be?