Sound: Zombies will be able to hear player movements. This means that the closer the player is, the more likely the zombie will hear them. Players are easiest to hear while sprinting, firing a weapon, or using a melee, also another thing to note is the movement you make in buildings can be heard by zombies and players alike, although a zombie won't hear you on the top of a building (depending situation) players will hear you clear as day, With this said when looting stop and listen for footsteps often especially in big cities it may just save you in the long run.