Sompsin's "Silence" is about how calm and chaos can slip into each other. The speaker begins on a hill, thoughts slow and precise, breathing steady. There is a hint of searching in the question "where have I been?", as if the quiet lets them look back and wonder. Then a sudden "crash!" breaks in, and everything changes: thoughts race, the heart pounds, breathing speeds up.
What makes the poem interesting is that the speaker keeps saying "I can't hear." First it's because of the crash, but by the end the reasoning has flipped. There is noise within the silence, and silence within the noise. The two states stop being opposites and start to feel tangled together. Judging by the lines, the noise may be inside the speaker's head as much as outside it.
The mood moves from peaceful and reflective to tense and overwhelmed, and finally to something uneasy and unresolved, where real stillness seems hard to find.