Why can't I use "free soundtrack music" in my podcast?

The reason why music from freesoundtrackmusic.com is NOT available for use in podcasts or on radio is that sound recordings (with no visual component) are treated differently by copyright law. Freesoundtrackmusic.com is a budget service intended to provide music for the soundtrack portion of video, film or multimedia productions. The licensing of music to be used in this way is called "synchronization licensing" and has a different set of legal rules which do not apply to audio-only productions: Audio-only means "sound recording" and is subject to the copyright rules of that format. If your productions are primarily sound recordings, I would suggest trying some google searches on "music for podcasts", "background music for radio" or "stock music for radio". There are a lot of music services these days, many of which may not have the same restriction against "audio-only" productions such as mp3 podcasts.