Just posting a reply here since I'm having the same issue as well and none of the fixes mentioned by others has worked so far. The only thing I have been able to do so far to help has been to mute the Master Volume in the settings so that when I enter combat or heavily populated areas I don't start stuttering. I even tried to mute everything except for the system sounds so that I would still be able to hear the alarms for timed gathering nodes and eventually if I was in a dungeon when the alarm pinged it would suddenly begin stuttering again.

The most annoying part is seeing everyone talk about how good and great and wonderful and amazing the music is in all the new zones and I can't even have the audio for an alarm timer enabled because it'll start making things wonky. It's not like we can realistically stay out of combat either, unless you're someone who spends hours on end doing emotes to other people in town. Even though I'm not some kind of audiophile who is necessarily missing out on a lot from not hearing the BGM, having to experience combat with no sound really has made me realize how much the combat audio helps my gameplay. I have a new found respect for any deaf gamers out there. Although, it is nice being able to do a hunt train without hearing that 1 annoying squealing female mi'qote that always seems to end up right behind me no matter what server I'm on.