Mine was a grunter, too. I was so excited about our decision to co-sleep, and then the grunting started, and I thought, "Oh my gosh, how am I supposed to sleep through this?" She grew out of it around 8 weeks. I read once that newborns are always in one of several "states" and one of them is "active sleep." The active sleep stage is the one where they are asleep, but they may be grunting and flailing their legs and arms all over the place. I think it is normal for them to spend a stretch of the night in deep sleep, and then small stretches of active sleep. I think I remember reading that active sleep helps their brains develop. Hard to sleep though when you are tuned to wake up at every little noise.