They are attracted to smell as well as sound

i was making no sounds and there's no smell, also happen sometimes that i heard a ominous sound and then an horde of fast zombies stat attacking me randomly from nowhere, like it was a random event generated by the game.. but that's totally out of control.. you can't survive

also a fyi the game currently will random spawn a runner near you randomly. this is probably the one that is throwing you off. it will spawn around 15feet away and just charge at you. it happens 2-3 times a day.
its the sole reason right now i dont feel like playing after loosing 6 hour game just cause game kept spawning runnners to throw at me for no reason.