Bizarre Sounds from Frozen Lake Explained

[C C]

http://www.livescience.com/48309-acousti...rocks.html

SNIP: A self-proclaimed "professional YouTuber" has scored a viral video hit with his discovery of the sci-fi sounds produced by skipping rocks across a frozen lake. The winter phenomenon is old hat to kids from cold weather states, but for Cory Williams, the eerie pings and pews were jaw-droppingly bizarre....

[Magical Realist]

I wonder what causes that. I used to skip rocks on rivers and lakes and never heard a sound like that.