foster dog barks everytime a door closes...

Hi. We just brought home a foster dog two days ago. He is awesome - but every time a door closes he freaks. he jumps up from whatever he was doing and starts barking like someone is attacking him. We try saying his name, whistling, anything we can- but he is in some kind of trance and doesn't stop barking. It isn't just our front door and back door either. We live in a twin house, and if he hears the neighbors close a door, he freaks out just the same. If he hears a car door outside, same thing. Even if he hears it on the tv, he barks. Sometimes he will just start growling at nothing.

The dog is a 5 year old male, neutered, boxer/lab mix. He is a great dog except for the barking thing. The spca says its because he is in a new home - but his barking doesn't seem to be slowing at all, it seems to be getting more forceful each time. He doesn't jump on anything, he just runs to the door and starts barking. I know he is protective but this is a little ridiculous.

Any ideas on what we can do to get him to relax and not freak out? I just wish it was easier to get him out of the barking state. If we could get him to calm down, I am sure it would be easier for him to start barking less. Maybe something happened in his other home, but its really starting to bother us because he will do it all hours of the day.

If you have any suggestions please let me know!