If you have Near Infinity, use the dialog.tlk editor (Edit > Dialog.tlk) to view the new dialog line with the sound in it. Make sure you can click on the sound and see it in the resulting dropdown list. Also make sure the Entry Type variable is set to Standard Entry(3). I believe a similar method exists in DLTCEP.
You didn't mention if the sound is actually playing. Is the stutter in the game's framerate, or the sound? Is the sound playing from inside a dialog, as in while you're talking to the NPC? If so, is the dialog flagged to pause the game?
Try copying ELLESI04.WAV to the override folder, though I don't see how that would help. Also, make sure you have a zero and not the letter O in the filename.
Make sure you have the latest version of WeiDU.
Probably not much help, but I figured I'd take a stab at it.