I actually suggested this in [another thread](https://sound.stackexchange.com/questions/1975/suggestions-for-a-tensioned-rope-effect), but for a tense rope sound effect.  But trying stretching leather with your hands or thumbs as a base for the sound. Then maybe add some splintering wood.  Pitch shift around until you find the right pitch, and work from there. 

I think somebody else in the same thread mentioned a Wicker basket (credit to that person).

Hope it helps.