The Question and Answer section for Robert Frost: Poems is a great resource to ask questions, find answers, and discuss the novel.
The word "something" refers to nature or perhaps even God. The idea is that there is an otherness that regards the wall in some way.
I always feel the sense of silence in this poem. Even the imagery is still and quiet. The mood has a surreal and reflective quality to it.
I'm sorry, you haven't provided the titles of the poems in question.