This happened to me couple of times. I hear the zombie screaming(!) but when I stop and look around there is nothing. So I continue to run to the direction where I want to go. I hear the voice again. And look around again. I am sure there are absolutely no zombies nearby. This can repeat itself couple of times.

Sometimes this just happens and there won't be any zombies around and you just continue playing. But sometimes, something hits me and I start bleeding. I can see the zombie only after that. And it always opens wound at first hit. I died becaues of this 2 times.

1st one I killed the zombie after I started bleeding. I found a nice place started applying bandage and I stopped bleeding. Then another invisible zombie hit me and became visable and of course I started bleeding. I killed the zombie again. Applied bandage again. Stopped bleeding again. But.. Another zombie hit me. Again I started bleeding but this time I died.

2nd one happened today. I was running to place when I heard zombies. I checked around as usual there was nothing. Then I continued running (actually sprinting) . But out of nowhere, I was hit the screen got blurred. I started bleeding. I found the zombie and killed it. But this time I couldn't use any of my bandages. And I had loads of them. So I died bleeding.

I'm sure this has nothing to do with my draw distance or such. Because I can normally see zombies or players far ahead.