Might this wood knocking event come from the bf themselves, a sound they are producing? Reason I ask is that in January, there was 18" of snow on the ground. To find two dry sticks to beat together......unless they carry them with them. I havent found anyone witnessessing this wood knocking, in my web searches. Has anyone read of witnesses?
My understanding is the sound is wood on wood. I know someone that has been close to this. If you're close to the action you will hear much more than just knocking. One may wish to have a change of pants in the pack.
