Sadie has a frustrated/annoyed/IWANTHAT grunt thing too and has for over a month. It was REALLY annoying the first 2 weeks and then it got a lot better. I think once they realize they can make a new noise or something they do it nonstop.

It got even better when she started sitting up on her own. I leave her with a bunch of toys on the floor and shes hapoy for a long time like that.