Here is a brief excerpt from the Cornell web article about the Ivory-billed Woodpecker at:

http://www.birds.cornell.edu/ivory/story2.htm

Sounds
On two other occasions, observers heard what might have been sounds of Ivory-billed Woodpeckers, but without visual confirmation.

  a.. November 9, 2004: Marhsall Iliff, a long-time birder who has extensive knowledge of Campephilus woodpeckers (the genus to which the ivory-bill belongs), heard 18 double-knocks that he identified as sounds made by an Ivory-billed Woodpecker. During 13 minutes, the sounds came from two directions. It was unclear whether the sounds were made by two birds, or by one bird after switching locations. 
  b.. March 7, 2005: Two observers simultaneously heard double-knocks at the same time. 
Way to go Marshall. I guess we know where you'll be heading back to in the near future.

Ed Boyd
Westminster, MD