As the title says.

To be honest with you, while having the characters repeat select words over and over again in the midst of conversation was amusing for a quick minute, it very rapidly became an annoyance.

I don't have any crashes or error messages. I've read multiple forums and actually found that the opposite of their advice (turning off 3D acceleration) actually helped with the issue quite a lot. I find myself unable to navigate my AMD Radeon graphics driver menus to find how to turn off AA for TLJ to see if that will help, because there only seemed to be an option to have to set to either "performance" or "quality" settings. Obviously, I'm looking for neither. I'm looking to turn it off. But it has been set to "performance" setting, if that matters. The game runs very, very smoothly and quickly despite this particular issue.

I'm hoping somebody will be willing to help me out or have some fairy godmother/father-like magic to assist me because, while I CAN play the game, it grates on the nerves. This is the first time I've ever had a problem with an older game that I couldn't quite figure out on my own, honestly.

Does only audio stutter or the whole game?

I've played this game on an Nvidia card with AA enabled through the driver's settings. I did get occasional game stutter, but nothing game-breaking until the very last level where stuttering made TLJ unplayable so I had to disable AA.

In Catalyst Control Center under Gaming\3D Application Settings select System Settings. There you should find controls for AA.

Mostly just audio. You notice extremely minimal lag of the character models/background, but it runs pretty smoothly nonetheless. So it often looks like April is talking normally, but she keeps stuttering over her words. Kinda funny, really!

Ah, thank you! I seriously couldn't find where the AA settings were. I will see if this resolves this issue.

Pardon for the double post.

Well, that didn't solve it. Completely, anyway. Apparently, for my video card, you can't disable AA, but you /can/ make it so the settings are controlled by the application. I figure by enabling that option it would solve the issues since AA isn't even a thing in TLJ, but no.

I'm not quite sure where else to go from here, really.

That's correct. What this control allows you to do is to enable AA for all 3D applications or on per application basis (useful when a particular game does not support it). If you set to Use application settings then the driver will implement AA if and only if you enable it in the application itself. Since the latter option is set by default, I'll assume that there was no AA enabled for TLJ to begin with, which also means it's not a culprit for the problem.

As to where to go next, I'd look into the sound driver itself and some audio options in Windows and TLJ.
In TLJ config dialog under Advanced there are some sound controls, try changing them. Also, I found this old post http://forums.steampowered.com/forums/showthread.php?t=1394211