Girls, hello! For three weeks now, the baby started making a sound like…

Girls, hello! For three weeks now, the baby started making a sound like "mmmmm" when he wakes up. It's not really crying but it's not cooing either. I can't put him down. He turns over in bed and makes that sound again. I take him out of bed, lay him down, and he makes that sound again. In the stroller, he falls asleep if you're rocking him. Is this normal? Or could something be hurting? Are his teeth? But his gums aren't swollen. I've been using gel for it. I haven't noticed any changes in behavior. Just so... I'm desperate