it took them quite a while to become aware of the faint whistling sound , for they were utterly dazed and spent and their ears still rang from the dissonance of the worlds final agony , but little by little they all raised their heads , first hearing the eerie silence and then , in its depth , as though coming not from some external source but from within their own frenzied souls , a faint , high-pitched whistling that grew steadily louder .