my ds is 3 1/2 months old and has recently started making this sucking noise almost all the time. his lips will move like he's feeding too. i thought, hunger cue perhaps? but he does it almost all the time and when i wait to see if he gets more whiny for a feeding he is actually fine (and he's the type who will really start wailing if he needs that feeding). does anyone else have a lo who does this?