Tennyson's use of onomatopoeia throughout this poem helps to create the effect of a brook bubbling, like the titular brook, down a valley. Tennyson uses alliteration—a "sudden sally" and a "sparkle"—to create images that appeal to the sense of hearing, as well as to create a visual picture. The alliteration on "s," and particularly the word "sparkle," seems to echo the splashing sound a brook would make if it were moving quickly and lightly, indeed in a "hurry" down the valley. Other onomatopoeic words that connote the sounds of a stream include "chatter," "bubble," and "babble."
The poem's rhythm and meter help to contribute to this effect, too. The short stanzas and near-hypnotic rhythm help the poem "draw [us] along" as readers with the brook as it flows. Repetition and parallelism, too—"and here and there," "the brimming river"—replicate the sameness of an ever-moving, repetitive stream repeating the same motions over and over as it flows.
The idea of the brook as a musical accompaniment appears explicitly toward the end of the poem, as the speaker suggests that it makes "the netted sunbeam dance." Words like "slip" and "slide" also suggest dancing, a sort of rhythmic motion which would accompany the continuous sound of the brook.