In Raymond Moody's classic book Life After Life(1) he explores the similarity of experience among those who have returned from near-death. During the early stages of the experience, many people report unusual auditory sensations (often concurrent with the appearance of a dark tunnel). One man described "a really bad buzzing noise coming from inside my head," while a woman heard "a loud ringing." Others have reported more pleasant sounds-- such as the tingling of bells, and a majestic kind of music.

1. http://www.amazon.com/exec/obidos/ASIN/0062517392/ctoc