Some locations, mostly towns and castles, will have dog kennels watching over areas. While the dogs are not immediate hazards, their barking will quickly alert nearby NPCs (both enemies and allies), drawing them to the source or the sound. They are always aware of the player's location, but only bark once they get close enough. Their "barking range" is roughly similar to a watchful/alert enemy's vision range.
Dog kennels can be pulled or lifted with the grapple hook, or picked up and carried. If picked, the proximity of the player will make the dog bark at least once before they cower inside the box.
The loading screen advice concerning dog kennels is incorrect in some details: toppling over kennels will prevent the dog from barking *only* if they land upside-down, if they land sideways or diagonally the dog may still pop out to bark at players.
Another, more definitive way to get rid of the barking is to throw kennels into wells.