Section 14.221 of the Manual lists the elements of an online audio citation such as a podcast:
Podcast:
Darcy Steinke, interview with Sam Tanenhaus and Dwight Garner, New York Times Book Review, podcast audio, April 22, 2007,
http://podcasts.nytimes.com/podcasts/2007/04/20/21bookupdate.mp3.
Citations in a bibliography are formulated in a similar way to a footnote or endnote, but do have slight variations from the way a footnote or endnote is formulated.
Podcast:
Steinke, Darcy. Interview with Sam Tanenhaus and Dwight Garner. New York Times Book Review. Podcast audio. April 22,
2007. http://podcasts.nytimes.com/podcasts/2007/04/20/21bookupdate.mp3.
Sections 14.274, 14.276, and 15.33 of the Manual offer information on citing an online sound recording, but their guidance is minimal. The following example is taken from section 15.33, but there isn't a lot of explanation regarding why it is formulated the way it is:
Coolidge, Calvin. [1920?] "Equal Rights" (speech). Copy of 78 rpm disc in RealAudio and WAV formats from the Library of Congress,
"American Leaders Speak: Recordings from World War I and the 1920 Election, 1918-1920." http://memory.loc.gov/ammem/nfhtml
/nforSpeakers01.html.