It happens as host or client. Its usually gas rats or bomber rats making sounds after they are dead but it can happen with any special that makes noise except for loot rats.
This next part is a separate bug report but its also similar which is why im reporting it here. Way before patch 5.0 this bug also happens with gat rats that are killed as you are loading into a game they make sound like they are still alive when they are not and it only stops when you move far away.