Maybe there is some hint for the problem in /var/log/messages or in the dmesg log. You can also send a report for me to analyze it (go to KDE Menu -> system -> openmamba -> Generate a system report.
First make sure that you have tried all the mixer buttons and sliders. Then you can try installing kernel-mamba-sound-backport or kernel-mamba-sound depending on what you have currently installed to replace it.
