Discovery wobbles when yawing

[Monkeys lips]

Hi all

I've got a problem with my TBS Discovery when yawing. I've got the aerialmob endurance setup on it and when I yaw it seems to wobble. Pitch and roll are fine. I've tried adjusting the yaw gains and it doesn't seem to have any effect. I've calibrated the secs too and still the same. Has anyone seen this before or does anyone have any idea what to look at next?

It also makes a horrible noise right at the end which is why I stopped filming and landed to try and get it sorted.

My setup:
Tbs discovery with aerialmob arms
Naza lite (with the V2 firmware)
Hobbyking Afro 20amp HV escs
Tbs 400kv motors
Tbs 4000mah 6s battery packs
Rctimer 15x6.5 carbon fiber props

http://youtu.be/IdTkV0N388k