Powepoint files are essentially zip files. If you open the file with an application that can handle zips, (or temporarily change the extension to zip and use Windows File Explorer), you will find the audio files in a sub folder called Media.
Or you could use
http://www.gmayor.com/extract_images_from_word.htm to extract the files to your hard drive (note that this add-in extracts all media files not just images - I may make it more selective in a future update, but for the moment it will do the job).