EDIT: Sweet Mary, I figured it out!! There are some volume shortcut keys on my laptop - they've been the problem this whole time :/ I always thought that they just didn't work in ubuntu because there isn't any visual feedback when you press them. That said, should I "undo" any of the things I tried below?
Clean-installed roughly a week ago, and I had sound, but it suddenly stopped a while ago and seemingly out of the blue. I'm assuming the change must have happened sometime around when I was letting the update manager do it's thing. I'm chugging away on a Lenovo T-60 Thinkpad laptop, so the sound card is on-board.
I've tried this: No sound in 12.04 LTS ubuntu
The accepted answer here: Sound not working after 12.04 install
As well as
This seems to be a common problem and sometimes some of the guides don't seem entirely trustworthy, so if someone could point me in the right direction, that'd be excellent.