I've encountered problems like that (not OS specific or play specific), When I don't have the appropriate codecs installed, or they have become corrupt. Or it is possible that your sound isnt configured properly in mplayer? I've never used redhat, so i'm not sure what to do with it specificly. But in KDE i've had a problem where i've had to disable aRts sound server in order to get sound to play from certain programs. Didn't like aRts anyway, made everything fuzzy. Can find aRts in the KDE config center, under Sound, then sound server (i think is what its called). Hope that helps at all. Good Luck.