What Does It Mean When A Rabbit Makes A Soft Grunt Noise? Or When His Ears Moves Up Or Down?

I have a rabbit. He is very friendly and acts more like a dog. Follows me around the house and everything. I used to think he didnt make any noise. But when it is really quiet I can hear him making a soft grunting noise.
Also sometimes his ears are standing staight up and sometimes they are back. What makes the differnce? Are they saying what kinda mood he is in? If so which ear motion means what?