Ok, so I have encountered the same audio stuttering and delays that many people are posting about on here. I was able to fix them completely using the download and instructions found here http://www.thenexusforums.com/index.php?/topic/248968-possible-sound-fix-and-character-creator-issue. Oddly the file is actually some kind of patch for another game, but after using that download, my audio worked perfectly.

However, when I started the goodsprings quest where you fight the power gangers (or whatever it is), I encountered massive slowdown and the game became to laggy to play. I fixed this using the d3d9.dll file found here http://www.gamesas.com/index.php?/topic/1123822-potential-fix-for-npc-slowdown/. That file works brilliantly to fix slowdowns and my FPS is good.

Here's the catch: once I used that new d3d9.dll to increase my FPS, the audio problem returned! If i switch out that d3d9.dll for the one that came in the audio fix download, the audio problem is fixed, but my FPS go back to being crap.

I've concluded that the d3d9.dll file in your game folder is somehow related to both these problems (at least for me), but I can't come up with any way to fix both of them. When I fix one, the other returns, which is really frustrating. I've already tried setting FalloutNV.exe to high priority in the task manager and just about every other suggestion related to these two problems that I can find on here, but nothing helps.

Anyone got any ideas?

Have you tried playing in windowed mode? It can alleviate the audio problem.

I haven't played in window mode, although I wouldn't be surprised if that fixed the audio problem. UPDATE: I played in windowed mode and it does not fix the audio problem for me.

I'm more interested in how to solve this completely. Like I said it seems like that d3d9.dll file has something to do with both these problems so maybe someone with a little more know-how (than me, that is) could come up with a solution.