My newborn grunts in his sleep a lot. Is it normal?

My 2m old grunts and sucks his fingers loudly in his sleep. I thought he was hungry but he doesn't eat when woken up. It's really loud and so unlike my first child. He's burped and changed so shouldn't be gassy. It only happens at night and after ~2hrs of quiet sleeping. Then he makes noise until waking for his next feed. I'm not sleeping well because of it and we tend to wake him to eat to stop him after 3 or 4 hrs. My older daughter was sleeping 5+ hrs at this age. If it normal and when will it get better?