Have you tried with the headphones? Also, I have something like this going on with my Sony VPCZ114GX, there is a workaround posted for my model at this bug report: https://bugs.launchpad.net/bugs/960124 Basically involves loading up David Henninsson's hda-jack-retask from his ppa at https://launchpad.net/~diwic/+archive/hda and then try Wouter van der Graaf's workaround on comment #7.
As for getting the model of your sound card, I tried the below. Although the problem may be that your machine doesn't know what model to use for sound in the first place.
Found with: $ aplay -l ** List of PLAYBACK Hardware Devices ** card 0: Intel [HDA Intel], device 0: ALC889 Analog [ALC889 Analog] ...
Then to get the model to put in alsa-base.conf: $ gunzip -c /usr/share/doc/alsa-base/driver/HD-Audio-Models.txt.gz |grep -i "alc889" intel-alc889a Intel IbexPeak with ALC889A intel-x58 Intel DX58 with ALC889