In the middle of listening to the last episode dealing with Legolas telling the fellowship what he is hearing from the rocks, grass and trees in Eregion . I have to say that I beleive that the rocks do remember the Noldor and how they delved and wrought them. I don't think that they are remembering echos of other rocks or rocks distance from them. I think this because I also think when Legolas talks about the grass and trees not remembering them that that is because grass and trees are fleeting. Grass and trees die and have offspring, but the ones that did "know" the Elves have long ago left this world. Not so with the rocks, rocks can be worn down after many years, from weather, and moss/lichen, but the rocks that were around when the Noldor were there are also still there. That is why they remember them, and lament there leaving... to the grass and trees the Noldor are just a myth handed down from there ancestors. Just my thought.