Thank you for responding, Einmimiria.

1. Any time there is many players on the field. The issue is worse with more players, with ~6-8 being the minimum to be noticeable. Given these conditions, Eurekan NMs, hunts, and alliance raids are hit the hardest, but it is still definitely noticeable and jarring in smaller instances like trials.
2. None that are really noticeable. Framerate responds as it normally does.
3. Headphones through 3.5mm jack on stock motherboard audio
4. It does not.
5. Restarting the game, the computer, adjusting audio settings both in game and out.

PS: Both my friends report the same issues, I'll see if I can get them to post here but the basics are: one has a GTX 1080 Ti and nonstandard sound card, another has a AMD R9 380 and uses a DAC and headphone amp.
PPS: There are several bug reports that may be relevant to this issue, one in the new section, and one in the accepted section, at the time of posting