747 Yaw Oscillation
For what it's worth------ I think when this occurs that the airplane is out of trim and the autopilot is working against that. Pilots tend to 'plug' in the autopilot early and leave it engaged without ever checking to see if the airplane can fly 'straight and level'. Try hand flying at cruise for a few minutes and see if there is any 'turning tendency' while holding it level. You'll notice that by having to put pressure on the wheel. If there is, take out the tendency by using rudder trim. When the a/c will remain straight and level without any pilot effort on the wheel, plug in the autopilot and the continuous yawing will have disappeared.
I believe this is true for any swept wing jet.