I too just grunted DS out. About 20 minutes before DS was born, I started grunting and bearing down with each surge. I couldn't help either of those reactions. I wasn't so much pushing "down there" as my belly/abs were contracting and moving DS down and out. It's difficult to explain but there was nothing for me to think about, my body was just doing! The only things my midwives said were words of encouragement and to feel DS' head when he came down. The whole experience was great.
That was my experience, too, exactly! 20 minutes after the first grunting. Bearing down. There was no stopping it, no thinking about it, and my abs were doing it all. I tried to hold back as she was crowning because I was so scared of tearing (I didn't) but there really was no stopping it.