In my experience, manta cries do sound different that the other cries. To many LO, is their way of getting to sleep. Just leave them alone when they are doing their manta cry. The manta cry for my LO can occur soon after a put him in bed, when he is tired, or after he has tried to fall asleep on his own and has been unable to do so. There are times that my LO tries to fall asleep on his own or 20 minutes and when he is not successful, he just starts to do the manta cry.