Heidi is a beautiful jack Russell/min pin puppy. She’s had some issues with shows of aggression since I’ve gotten her(i.e. barking and growling at strangers on walks). For the most part I have been really proactive about this and it’s practically gone away. Instead, she’s a lot more tense at home. She’ll look out a window and just start growling, but nothing is even moving out there. There won’t be sounds, birds, cars or people, yet she growls and occasionally gets into a barking fit. This even happens occasionally when she’s nowhere near a window. I’ve blocked her access to windows but this isn’t a solution for long term. What could she be growling at and how could I teach her she doesn’t need to be growling?