the sound in general is lagging, about 5-10 seconds and the NPC's speech either doesn't work at all or will "catchup" if i hit the ~ key to pause the game, same for gun fire. the Game it self is not lagging at all so far, just the sound as far as I can tell. Music seems to work OK though...I installed the newest sound drivers available which came out on the 8th of this month for the realtek HD Audio, and the newest Nvidia drivers that came out on the 18th for my 8500GT, if needed I can post my dxdiag information.

I Have the same issues...can i ask if you leave the radio in the pipboy on.. does it stabilize the environment sound? It does here...as soon as i turn it off however , back to lag/catch up

I have not tried it with the pip radio on, I will try this though, have not played if for a couple of days because its so annoying...