If you want all the nitty-gritty technical goodies about the sound of "The Voice," check out what we've got to say in the "Form and Meter" section. But if you want the more immediate, and a little less scholarly take on the poem's sound, then read on.
To us, "The Voice" sounds like one big, repeated sob of a slightly-deranged person. All of the crazy rhymes and repetitions, the unusual meter, the lilting waltz-y sound of the poem make us feel completely dizzy and off-kilter when we read the poem aloud.
For example, rhymes like "listlessness" and "wistlessness": they seem a little overboard to us, a little contrived. They seem like the crazy ramblings of a guy who's off his rocker and losing touch with reality And as we read the poem out loud, we begin to feel how the speaker of the poem himself feels—slightly crazed, and definitely compelled to listen very, very carefully to the sounds he hears around him. The poem's use of alliteration ("much missed," "wan wistlessness," "faltering forward") and assonance ("thorn," "norward") only adds to the sonic jumble.
In short, reading "The Voice" makes us feel like we too are hearing voices from the beyond. (And, not gonna lie: we kind of like it.)