Its just like the fact that you will walk by a person 300 times in your life, and until you meet him you dont realize you pass him on nearly a daily basis. Now after you meet him youll see him all the time. Coincidence? No, its just now you realize what you are seeing because it makes sense to your mind now. To relate this to the call, maybe its a real call maybe its not. i believe its real, and its just an aggressive grunt. The reason noone never "heard" the sound before was because people just thought it was a regular grunt,or a grunt that came out to hard. And even when the sound was heard, the sound fell on deaf ears to say..they didnt think it was a total new vocalization.. which it may very well not be.. it may just be a grunt and it may have the same meaning as a grunt, but the fact of if a buck actually makes the sound is easy to see, they do.. And for the nonbelievers you have most likely heard the sound before yourself, and now that you listen for it most likely you will hear it again.