I got this kind of generic idea from a youtube video right here:
(idea is the key) You put a casing on the head of the arrow, then fit ammo inside it. when you shoot it the round detonates on impact, causing loud noise and damage on zombies/players. It would bring a whole new element on distraction against players and zombies. The arrow has a good range and the sound could be registered as a regular gunshot. Imagine you're in a tight spot inside town, zombies coming to your position and other players nearby. With this you can more easily give the zombies a new target somewhere else without giving up your position. Or of course you could ruin someones day by shooting the arrows to their position maybe leaving them surrounded by the dead! I think its a nice base for an new idea. How it would fit with the gameplay is something i cant tell but its still an interesting idea :)