We had our first house guests (inlaws) stay with us since we have had Axel (5 months). They stayed four nights and Axel is friendly as usual, however when I get up in the morning early and take care of the dogs needs, and he is relaxing on his blanket he starts to growl and look upstairs when he senses movement from my inlaws on the next floor, he will bark and growl when they come downstairs, and even start a very low growl when he here's the toilet flush or water turn on in their bathroom. He has been like this for the 4 days they have been here, however he is totally fine once they come downstairs and he smells them and they pet him etc. Have any of you experienced similar experiences? Is this normal behavior? Protecting the house? I understand after the first couple days, but still doing it after 4 days seems kind of strange, I always give him positve communication like "it's ok, it's just grandpa and grandma, etc", but not sure if I should be trying to deter this behavior or if this is an instinctive behavior? Thanks