Cliff Barackman has posted an interesting entry over on his blog, North American Bigfoot, in which he theorizes on the source of the wood-knocking phenomenon. Barackman writes:
I'm calling them knocks, but I do not think these were the sounds of wood on wood. The pitch and timbre of the sounds remained constant the whole time. This would not be true if a sasquatch was beating on trees as it passed: each tree would sound at least a little different than the one before, and at least some of them would sound very different. This simply was not the case. I have often wondered how sasquatches can answer my own knocks so quickly. It takes some time to find an appropriate knocking stick, as well as a suitable tree to hit. So much time that sasquatches are clearly not going through this process.
I think they are clapping. That is not to say that they never hit sticks against trees. I think they do, but many times they are very likely clapping.
I theorized back in May of this year, in my post More Thoughts on Wood Knocking, that the sounds being heard in the forests of North America, and thought to be wood on wood, might, instead, be the sound of hand clapping on the part of the sasquatch. This, as is pointed out in the first part of the article, is a communication technique used by known great ape species. The hand claps were used by female gorillas to get the attention of their young and also to alert the male silverback protector of an intruder's presence. Interestingly, one way the big males responded to the hand clap "alerts" was by taking a large branch and banging against the base of a tree in an apparent attempt at intimidating the human intruders. Barackman's thoughts mirror my own in many ways, though he states things much more eloquently than I.
It was good to read Cliff's thoughts on this. You can access his article here. The title of this particular entry is "Bluff Creek 2009". Cliff's thoughts on the source of wood knocks are near the end of the entry.