The dialogue between Tirion and saurfang has no audio since the launch of Icecrown, I recently played it as alliance and the audio plays for them.
It wasn’t playing for me as Alliance, I believe some raid addons / weakauras mute the RP.
Edit: Can confirm Fojji has NPC RP for the beginning, LDW, and Sindy muted by default in its Custom Options. Check that, if you’re running it on your Horde.
I thought an addon might of interrupted it so I turned them off before soloing the first trash pull, audio only plays on alliance for me and nothing on horde