My 8 week old baby grunts and makes noises in her sleep at night. What could thi be about?

My son did this too in the beginning. I also think it is just digestive, when it stopped I noticed it coincided with him no longer having bowel movements in his sleep. It is a lot of work for them to learn how to use their muscles to p gas and stool and I believe that is where most of the noise comes from. Believe it or not you might start to miss it when it's gone : )!