did you install the Realtek HD audio drivers from Realtek's website? if so check to see if there is a script to uninstall it in the directory you unarchived the original installation files. Alternatively if you were able to tick a box for the restricted drivers in ubuntu, then you can untick it to remove them.
Thanks! Your advice was helpful... but there was no shell script to remove the drivers.
Also, I have recently noticed that everything is working perfectly (the sound that is) apart from in google chrome!