I don't think it's aggression, but I don't think it will work itself out. I think he just needs to be trained what is an appropriate reaction when someone comes to the door. I allow my dogs to bark, maybe 3-5 times. Then loudly I say "OK THANK YOU!" and that's their cue to zip it. When friends come over I ask them to try not to get Coke worked up and give him attention and petting only when he has "four on the floor". Kenya is no problem, as soon as the door opens she backs off and just sits down or goes back to whatever she was doing.