Comment 36 for bug 1033299

... the bug is also in lubuntu 13.04

my favorite fix:

sudo leafpad /etc/modprobe.d/alsa-base.conf
... and added this line to the bottom of the file:
options snd_hda_intel index=1
... then reboot

From: http://www.lubuntutips.com/2012/05/lubuntu-sound-on-msi-x370.html

or

sudo apt-get install pulseaudio