Welcome to Yorkie Talk!
I'm sorry, I don't have the answer to your question as the 3 Yorkies I have had, have not been barkers. That's not to say that was normal. I just never thought much about it. Sounds like you're little one is vocal.
The one I have now rarely barks. A couple of times a guy came walking into our yard holding something in their arms and she got very vocal until I picked her up. For some reason she doesn't like someone (a man??) walking toward her with something in the arms. I don't know what that's all about. Strange.
Another time, I was walking her and we walked past a yard with a couple of those very large figures that people put in the yard during holidays, the ones that are blown up, and she stopped to stare at them then started barking like she was quite upset. I picked her up and kept on walking and she quit. I had to take a different route home. Go figure.