Mack's «silence» is about the strange weight of a quiet that used to be filled with sound. The speaker looks at a CD player and the rooms around it, places that once held melodies, and finds only emptiness. The music hasn't just stopped; it has been "drowned out by quiet," a odd, pointed phrase, since quiet normally can't drown anything. That small contradiction shows how overwhelming the absence feels.
The "thousand singing giants" suggest something huge and powerful, whether a literal wall of sound or a bigger memory of life and company. Now it is "reduced to nothing." The last lines break apart one word at a time: "but / deafening, / hollow, / silence." The slow drip of the layout makes us sit in the pause. The mood is lonely and heavy, tinged with loss. The speaker doesn't say what caused it, but the poem makes clear that this silence isn't peaceful. It hurts.