This sounds like barrier frustration. I have a German Shepherd in for training that does the exact same thing. It is very common with them. I’m guessing it is a very high pitched bark. She is mostly frustrated that she can’t go over to investigate. Leash manners and a formal heel is the way to fix this, along with a lot of consistency to teach the dog that the behavior will not get her anywhere. It might take up to phase 3 training if it is very pronounced. How are you doing with a formal heel command?