I know how you feel - my Sting did that. So, it could be another dog barking that is triggering her to bark. The dog could even be a block away. Or it could be a vehicle that sounds to her like the mailman, or UPS, or FedEx - if she barks when they come. Or someone is walking a dog - again that can be a block away. I did like you - I first checked just a quick look- then I told him to be quiet in a firm no more of this behavior voice. I didn't do the distraction noise, or hand signal. My concern was that I didn't want to reinforce his behavior by setting a pattern - he barks - I get up to look - he has to do something else. But I did step up his exercise and obedience work and his tug reward so he would have plenty of other things to do.