Ive heard a buck grunt very loudly like that. It was the largest buck ive ever seen, he was chasing a doe in dry leaves, and I heard him grunt several times before I even heard them running in the leaves, and then spotted them for the first time at about 100 yards, so the grunting I heard was coming from farther then 100 yards, it sounded like he was on a megaphone, it echoed through the woods like nothing I had ever heard. Kind of neat,, it was also the first time I ever heard a buck grunt.