I just logged in to a 40 man server in one of the apartment buildings in Berezino, the first thing i hear is like a horde of zombies, but i couldn't see any.
So i play for 5 minutes and then out of nowhere i get like 6+ hits from these invisible zombies, so i run away and bandage myself but the sound of them keeps following me and eventually they killed me.
This has happened once before but in Elektro but then it was only 1 zombie so i climped up in one of the fire stations and logged.