This is not an issue but a suggestion of improvement.
At the moment, when we arrive in one city or village, there are a couple of zombies guarding front doors of houses. Thanks to my axe, I can first kill some of them getting my loots "quietly".
It would be nice if sometimes and so randomly, there will be massive attacks of zombies (hundreds of zombies at the same time) inside one city and coming from anywhere. It would oblige the survivors to leave immediately the concerned city or the village. This massive attack should choose one city / village randomly every 30 minutes i.e.
When the massive attack starts, there will be a military siren that could be heard in the whole map.
When the village is inundated of zombies, they will simply die progressively if they don't find any people to kill inside - releasing workload on the Server itself.
I really think this new feature might increase the fear making the game very attractive :-)