This happened to me earlier this week. If you're on Xbox, from the Xbox screen select the d2 menu option and select quit game. The sound was back to normal after getting back into the game.
Yeah that worked for me, but it happened again after an hour, so I unplugged everything. It’s definitely on bungie’s end.
I also noticed it in onslaught when you were on spam ability boss rotations and there were a bunch of warlock stasis turrets and crystals everywhere and the game had mad packet loss and stuttering issues. That’s the only reason why I thought the new warlock exotic was causing it.