Just a question, but did you test the sound with the Live CD before installation? If the sound worked with the Live CD, then there must be a package update that broke your sound. If you have your Live CD handy, would you boot into it and test out your sound just to verify and make sure. It only takes a few minutes, but might help target wherein the problem might be.
Also, some people update via Synaptic. This method can break audio or video, as well as update to a new kernel. Updating via Synaptic might be something to reconsider. The regular and suggested method of updating Mint is via the mintUpdate application, and sticking closely to the Level 1 and 2 packages. It is possible that a Level 3, or if you have them enabled, a Level 4 or 5 package may be causing this problem.
I am just tossing out some ideas that might be an easy fix. If it gets more in-depth, you may have to wait for one of the more advanced users to make some comments.