This can be caused because you are playing on a outdated server. Thats why it
doesn't happen on every server.

I think that this is caused because you can hear the zombie sounds/drinking/eating even if it happens on the other side of the map. So whenever you hear someone eat or drink it is because someone is eating at that moment somewhere on the server. same thing with the zombies. But you shoudlnt get fueled though, I once heard a zombie randomly when I was in the middle of the woods far up north and I thought that it was this glitch sound effect but from nowhere this zombie jumps up at the air and slams me from the behind xD it scared the shit out of me.

EDIT: I was far away from a friend before ingame but we was talking with each others through skype and he could hear someone drink at the exact same time as I drank my soda.