Alternatively, you could go with more of the original mythos, and have the wail not be a killing attack (D&D popularized that), but instead be a notification that someone has died... or is fated to die. In the latter case, you could run it a bit like the barabbas curse... or you could run it as a warning, and say that - if the hearer heeds the warning - free will allows gaining a bonus versus death. (I.E. free will trumps fate, so if you're warned, you can actually do something about it.)
I could also see an alliance between a banshee and a valkyrie - the banshee figures out what important people are going to die when, and the valkyrie goes to collect...