I have experianced the same sound except what i heard was almost a thunderous deer grunt two times in a row repeatedly and it never moved away but instead either stalked me home or put on flanking manuvers.
I have heard it at least a dozen times and have spotted it on two different occasions and i have not been the only witness to these events.
Some of my ex-millitary friends and myself have been hunting the creature for some time now and when i first started off i believed there was only one but soon realized that there was two then learned that it was two adults and one juvinile and after a group from a bigfoot society has came down now i believe that there is at least 4-5 if not more from the sounds that they were making and where they were coming from simotaniously.