The sounds ice makes as it plummets down a borehole is strange, to say the least, as you can see from this video:
And if you're curious about the reason for these sounds, there's a good explainer here from Mark Bocko, professor of the electrical and computer engineering department at Rochester:
As the piece of ice falls down the hole, it scrapes and bounces off the edge of the borehole. You can hear the frequency of this sound decrease as the ice chunk picks up speed the further down the hole it gets. The decrease in frequency is the Doppler effect, the same effect that causes a car horn to drop in pitch as it drives past you.
After the ice chunk hits the bottom of the borehole, you can hear a "ricochet" noise, which is caused by the slightly different ways the sound from the impact propagates back up the borehole.
[Via Boing Boing]