No sounds when mounting, looting coins, DBM/GTFO addon warning sounds etc.
I also got some really choppy sound during the Battle for Razor Hill quest when it started. Voices from Vol'Jin and Thrall and the music was really choppy until I got to Razor Hill. It disappeared from time to time. Sound seems to behave bad when there are a lot of sounds going on.
Seems there are a few threads about this on the US forum as well. There's a temporary fix if you need the warning sounds from addons. Go to System > Sound and temporary turn off music and sound effects.
My sound card is an Asus Xonar DS with the latest drivers.
A bit OT: I noticed that reward items from heroic scenarios doesn't display on my character when I logged in here. :P