Thanks for the suggestions. I can give those a try.
"Unless you have actually seen the deer as you heard it grunt softly, I'd suggest that it might be a doe's vocalization you are hearing. I've heard does on several occasions making soft "contact" grunts to keep track (I believe) of their fawns in thick cover."
That crossed my mind as well.
"I also think that grunting to a deer that you've seen and is also very close is risky to do, especially from a tree stand."
I'll keep this in mind. Thanks.