So just over a week ago our 5 month old started barking at noises. He's been slightly vocal as a pup, he'll play-bark on occasion, but lately he's been barking at noises from the TV, or even when the A/C turns on, especially if he's tired or if he's been sleeping and a noise wakes him. He does it multiple time a night too. He always faces the front door, and won't stop barking until we walk down the hall to the front door with him. We've tried telling him "no" or "leave it" but I'm not sure if that's the correct way to stymie the barking. He's obviously scared and/or startled, but I don't know if there's anything we can do. Any suggestions?