Nelson, sounds like either a really short sound file or a file that gstreamer can't play for whatever reason, as you discovered already. I make no guarantees about compatibility of sound files for it, so while it's not the expected behaviour I'm not going to consider that a flaw/bug with flipclock itself... if you find a common trait between the songs that don't work though let me know I can try to see if there are any known bugs/workarounds for gstreamer...