Can someone explain how the runner system works?

[Sountrex]

OK before you explain the basics here's what i am baffled about and what i know.

What i know about runners being spawned:

-A lot of noise!

-Those fat guys that explode

-A random explosion for example if you shoot at a barrel or shoot your gun in general

-Demolisher rocks/ Excavator mike rocks? From what i can see they do noise.

NOW Here's what i am confused about.

I kill a zombie right? Typical. My weapon has electric and fire modifier on it right? Yet SOMEHOW when i kill a zombie i get farted on or something and my screen turns green, i take damage and then like 4 runners are spawned with their distant screams.

Not to mention when i just stand still around a building to enjoy the scenery, something random explodes with no reason explained whatsoever and then runners are on me again.

This began to happen shortly after i did a few of the main story quests, and i'm going for 100% run so i did all the sidequests and up until that point i've NEVER seen these things happen?

So... How do i get (literally) Puked on by a dead zombie that then 'explodes' and intoxicates me and spawns more runners? And no! Not the green zombies only do that. I've killed normal infected without the green thing and it still happens, i'm genuinely confused!!!

[Twinkletoes]

I hate virals(their name).

So here is how I understand it and what might be happening.

virals spawn when noise is made, normal. City is not static so there is always something making noise(some zombies are on fire and can set explosives off). Problem is when they spawn they don't care about the noise that lured them, they go for you. You can't make noise and sneak away, they know where you are and they are coming for you.

I know what you mean about the stink cloud. I THINK it only happens when you set fire to the poison zombies(I think the green screen is you getting poisoned for taking a whiff). Also it might happen at random because.....faulty triggers? Not sure, someone might of made an oopsie when coding the game.

I think it is the smell that attracts these runners. Honestly this sucks because it makes fire a BAD elemental effect.