Gunfire Attracting Zombies

[Bouzouki]

Hi and thanks in advance for any info.

 

There was a time I played and firing a weapon meant that Zombies from all around would converge. It made it scary to shoot in a house for fear of getting trapped...  we miss that and I cannot figure out how it was even like that to begin with. Did I have a mod? I can't remember.

 

Are there any mods that you know of, or a hint on how to approach making one (I have modded before...  but not something like this)?  We want stuff to come after us if we were so brash as to discharge a firearm or throw a bomb. 8P