They were showing the herd mentality of the walkers. A walker that sees or hears something that might be food starts heading in that direction. It doesn't matter if the noise stops, it still goes in that direction. Once set in motion it'll head in that line of direction until it finds someone to eat, or something else gets it's attention. Worse, other walkers that see a walker moving in that direction will then start moving in the same direction. Then you get hundreds, thousands, moving in the same direction until they make a herd of walkers that can swam over locations. Get a large enough group, and then they'll spread out enough that eventually one will see something or hear something and then move in that direction, dragging the rest along with it.