Not sure what is causing this, but WoW Classic is sending a crackling sound into my headset since the update. I am using Steelseries Arctis 7 and I was able to isolate that the game is sending a sound and it sounds like the headset is crackling. I tested this with other audio sources and it only comes from WoW Classic since the update.
Had this issue occur to me a lot in WotLK pre patch and eventually seemed to go away on its own. Believe it had something to do with DK voice. Has happened on Algalon once or twice also since then. Spent hours looking for a fix and only thing I found that worked was a temp fix and had to be re applied every time it started crackling.
Fix was to make a macro in game and use this “/run AudioOptionsFrame_AudioRestart()”