Report 43973: Canoers report a rock throw and possible grunts near Grand Marais

I had gone to the Boundary Waters canoe area in Minnesota August 18, 2013 with a friend. As we were canoeing the first day, it got dark. It was around ten pm and we were in the middle of a lake when we had a rock thrown at us. It was thrown a good 150 yards from shore. Then about twenty minutes later as we back tracked to the car, we were in a small canal between two lakes and heard a strange noise that to me sounded like a cross between a gorilla and a duck. The noise was about 30 yards away from us. We heard it for about ten minutes and every time we shined our flashlights towards the sound,  we could not see anything. We had been sitting there for a while due to our canoe getting stuck on rocks.