The Fortean Times has published an online article about EVP, or electronic voice phenomena, the experience of hearing ‘voices’ in the background of sound recordings.
The author of the piece has experienced EVP and believes the sounds to be spirits of the dead trying to communicate through the static.
Whether you believe this explanation (or think that EVP is more likely due to apophenia) the article remains a fascinating description of the history of the phenomena, most associated with parapsychologist Konstantin Raudive.
Link to article ‘Distant voices’.
Link to wikipedia entry on EVP.