I am probably most of the views that you have seen, I have been checking on the thread since you posted hoping that someone can answer you.
However since no replies have come in yet I went ahead and booted Ubuntu to attempt to assist you with your issue.
To view the package installation history you can open /var/lib/dpkg/info in the file browser, then view it in detailed view and sort by modified date, this will show you the order and dates that the packages were installed.
As for the sound problem, I have been hearing a lot about it, but have not experienced it. One thing you can do is guarantee that in system -> Administration -> users and groups your user privileges include "use audio devices". But most reports are saying that the audio problem is not related to any specific changes but that it is random due to instability in pulseaudio. I have not had any issues so I have not been able to test this, but someone posted a script at http://www.commandlinefu.com/commands/view/1890/fix-ubuntus-broken-sound-server that is reported to fix the problem when it happens.
Please report back telling us if the script works and stating any other information that you may have come across, hopefully together we can find a permanent solution.