Norn Engi Animation Bug
I had the same issue on a Charr character. If you hide the aviator’s cap it will stop.
I was able to reproduce this with 3 different computers; it’s an error in the animation itself, not your PC.
Same issue on my Asura. Hiding the Aviator Cap or switching to an Outfit stops the glitch.
I don’t frequent the forums too often, so I apologize if this is already a known issue.