Moaning himself to sleep

C

For the last maybe 2 weeks, my 5 months old has been moaning himself to sleep. Let say my husband and I are trying to put him to sleep he’s making that moaning sound. He also does it when he wake up during the night for maybe 5 minutes and then falls back asleep. He’s not crying or sick or anything. Is that a way to sooth himself? Is it normal ?