An explanation of why it makes such a great “pew” sound at the end. The cylindrical bore hole acts as a waveguide, in which acoustic waves travel. Waveguides reduce loss of energy in transmission, but the speed of the traveling waves in a waveguide (the group velocity) varies with frequency, with higher frequencies traveling faster. This phenomenon is known as dispersion. When the ice chunk hits the bottom, it produces sound over a broad range of frequencies; we hear the high frequencies first because they travel faster, and that makes the distinctive pew sound.
You can also hear an example of dispersion if you do a Google video search for “stones skipped across an icy pond”. In this case, the sound is traveling via bending of the ice sheet, which is also dispersive, and makes a similar pew pew sound.
