Check these links for a possible solution.

Wikipedia page of editing software
http://en.wikipedia.org/wiki/List_of_free_software_for_audio

Audiobook Cutter (3 versions)
http://www.audiobookcutter.com/

Mp3splt
http://mp3splt.sourceforge.net/mp3splt_page/home.php

If you have the patience "Audacity" will do it for you but not automatically.
You will need to download LAME to export mp3 files from Audacity.
(Go to the Audacity web page and go to the page for your operating system. )

http://audacity.sourceforge.net