First of all, congrats on getting that far!
Apparently you aren't alone in having sound coming out of the mic socket. See also
http://www.linuxquestions.org/questi...threadid=52588
I have a Soundmax AC97 also, and use the Alsa sound system, which I think is not standard on RH/Mandrake. Everything seems to work OK.
If you can live with the problem and no-one can suggest a quick fix you might be just as well accepting it until your hardware gets better support.
If you want to look into Alsa at some stage, see:
http://freshrpms.net/docs/alsa