In an urban environment I suspect sound above 20KHZ. Try to find a Boston Terrier and watch it's ears. These dogs hunt by ultrasound so sounds we cannot hear are in the sweet spot of their ears.
The other possibility that comes to me is a smell. Like a meth lab other chemical concoctions. Does your dog act normal outside the area where you live?
55 posted on 09/02/2014 3:34:19 PM PDT by SpeakerToAnimals
(I hope to earn a name in battle)