Starting with 2.06, if your mission tries to play a sound and it's missing, by default all you'll hear is silence. This is how it was in 2.05.
Since some of you might be working on missions and testing them with the 2.06 beta package, I thought I would bring it up here that you can debug any sounds you're not hearing by setting the following cvar in your Darkmod.cfg file:
seta s_playDefaultSound "1"
That setting will cause a tone to be played for a missing sound.
Starting with 2.06, you don't normally want to play missions with that cvar turned on, because existing missions might have some missing sounds and no one wants to hear beeps or boops that are out of place.
But for debugging purposes, you and your beta testers will want the cvar turned on to suss out any missing sounds.