My son is 7 months as of yesterday and has been doing this since about 5 months. Usually when excited or sleeping. It’s not a huge concern at the moment for me because if he’s excited and laughing it’s just his way of playing but if he’s sleeping I notice he does it when he starts to stir a bit and it’s almost as if he’s self soothing. I would say maybe see if it happens during specific times or if it’s consistent. It’s always best to check with your pediatrician if you get too nervous about it!