The downside of being the top floor flat is that we have windows on all sides. Why would this be an issue? Because it means Kobi has just that many more windows and ends of the house to patrol and become barky at.
We live in what I considered to be a quiet neighbourhood (I grew up on a bustling main street in the north end of Halifax so yelling, screaming, sirens, honking and every other imaginable sound was constant.)
When we adopted Kobi we were living on a quieter street, much less traffic and foot traffic, but had thunderous neighbours above and beside us, so in reality it wasn't quiet at all. And strangely enough, Kobi never barked indoors.
Barking at strange sounds started shortly after moving to this apartment. The sounds of people slamming their car doors particularly bothers him, as do car alarams/honks, people talking as they walk by, jingling dog tags, dogs barking and a whole slew of unknown and inaudible sounds to our ears.
Having the windows open to cool the place off has not made things better. But unless we want to suffocate in humidity, the windows are staying open.
I have yet to successfully find a way to discourage Kobi's barking, but hopefully moving just a few blocks over in September will help.