straining/grunting noises at 4 weeks

My little man has been making straining/grunting noises, almost like he's pushing out a poop he isn't constipated and when making the noises isn't pooping 😂. He's not trapped wind as we always make sure we get it out. He not in any pain. Eats and sleeps still just, just every now and again though the day and night makes these sounds. My other half said oh I think he's in pain get him out and wind him, but he goes back to sleep once he's made the sound. Just wondering why this maybe. I have read that it's fairly normal. Just wanna see if you hot mamas have experienced the same and have any advice for this worried new mama.