This seems to mostly affect the area where the Deathshades spawn and is less pronounced down in the actual arena, but whenever I’m standing on top of the east side of the (outdoor) Theater of Pain, where you accept the daily “Bet On Yourself”, and Xantuth is active, his Deathshades appearing and flying past trigger an EARTHSHATTERING sound.
I think it is a modified version of RaidBossEmoteWarning, SoundID 12197 https://www.wowhead.com/sound=12197/raidbossemotewarning as the PlaySound function seems to get called most of the times the Deathshades swoosh past, but sadly not every time.
I tried using the addon MuteSoundFile to mute this sound, I tried writing code that would mute SFX by setting the CVar when the sound is played, but nothing really works. I settled on a script that mutes sound every time I enter the subzone “Challenger’s Promenade”, but that’s obviously a very dirty workaround.
Edit: observed Xantuth again, it seems the sound is played on the Dialog channel, which I have set to maximum to, well, hear the voiceover, compared to the Sound/SFX channel, which sits at ~30%.
This is obviously not a voice line that should be boosted via this channel.