If a melee weapon does 100 or more damage to a zombie in a town, it will make a different noise depending on the weapon and alert every zombie. Think about it, if a zombie dies from getting hit by a milkman’s shovel, it’d probably be pretty loud, considering that not even a revolver could do that. (Even if it’s not fully charged, this will apply. The only criteria is the weapon doing 100 damage in a single hit.)