To install sound drivers. This is ONLY if needed - Don't fix it if it's not broken!
sudo apt-get install dkms
sudo add-apt-repository ppa:ubuntu-audio-dev
sudo apt-get update
sudo apt-get dist-upgrade

sudo apt-get remove --purge alsa-base pulseaudio
sudo apt-get install alsa-base pulseaudio
sudo alsa force-reload (or just restart to see changes)