Ok I did some testing here. I was running in glide mode (with wrapper) at 1024x768 and exactlty the same problem occured. In short sentences it only played the firstt second of audio.
So I switched to 640x480 and same problem but I noticed that what I thought was a graphical glitch before was the blue ring resizing wrong with highres patch.
NOTE: I think I may know what the problem is with the blue oval. The highres patch is resizing it. Because the ring is aplied by the 3d engine it seems that it probably will display the oval without actualy needing a 3rd party rezize much like the cockpit Somehow the Highres patch is exponentialy increasing the size of the oval as the resolution is increased (this happens in both glide and D3D) This is just a guess but see the screeshot below for details.
Anyway that led me to believe that the Highres patch has nothing to do with the sound issue.
Partial Solution: I put sound hardware acceleration to none and the sound glitch all but disapeared. Turning sound acceleration on and even switching to D3D the problem returned in full force. Even so, with it set to noe it still happened once and a while, but it was more random and space out... like twice per mission as opposed to every line if dialogue. I don't know why this doesnt happen in standoff.
Note the light blue haze... aparently thats the resized oval