First off, the zone. The bug occurs at Coerthas, The Pillars, The Supreme Sacred Tribunal of Halonic Inquisitory Doctrine.

I can reproduce the bug as many times as I want.

When entering and exiting the Tribunal building, within a 10 or so yalms of the doors, abilities and spells activated produce no sound. I have tested using Swiftsong, Mage's Ballad, Foe's Requiem, Army's Paeon, Flaming Arrow, Sprint, Internal Release, Blood for Blood, Hawk's Eye and Raging Strikes.

Ability sound will resume either after the doors close or moving far enough away from the doors.

The trigger seems to be actually entering and exiting through the doors. Standing inside or outside of the Tribunal after the doors have opened, without entering or exiting, still produces ability sound.