Different desktop environments work with different sound front and
backends. Some work better or worse with different hardware. You
may have to experiment a bit. I would start by looking at hardware drivers
(additional drivers). It may want to update or say you have proprietary
drivers available. If that fails then I would try a different backend. Many
distributions use PulseAudio on top of ALSA. You can try removing PA and
using only ALSA. Some people find that if the remove PA it clears things
up. Others find that if they use Xine over Gstreamer it fixes problems.

You can try installing Kubuntu-desktop from the repositories and switch at
login to see if sound works there. The reason to try this is because KDE
(the Kubuntu desktop environment) uses a different sound system. It uses
Phonon and Knotify. If the sound works in KDE then you know it is
likely something at a higher level. If it does not work then it is likely a
driver or low level issue.

It is a confusing situation. See this chart:
tuxradar.com/.../how-it-works-linux-audio-explained