There is a trick to accessing the weights.2 Open the Keyframing Tools rollout and click the Manipulate
SubAnims button.
The Motion panel now displays additional rollouts for Position List, Scale
List, and Rotation List.
3 Scroll to the Rotation List and select the Layer->Noise Rotation.
Now you're ready to animate the Weight field.4 Turn on Auto Key
5 Move the time slider to frame 70.
Using Controllers with Biped | 835