The first sound affect ("Gr-r-r-there go") serves to set the tone and intent of the dramatic monologue poem "Soliloquy of the Spanish Cloister" by Robert Browning. There is no mistaking the meaning of "Gr-r-r." The poetic speaker is angry ans deliberately feeding that anger. The last line in the second stanza might well be said to contain a sound affect--the sound affect of alliteration. The recurring /s/ in "Swine's Song" dramatizes the spiteful ill-will the speaker feels for the poor monk who is tending his garden and minding his own business. The next sound affect ("(He-he! There his lily snaps!)") goes a long way to showing the maniacal nature of speaker. Line 70 in the IX stanza might be thought of as sound affects in the same way as "Swine's Snout" is, especially since two of the words have meaning: Hy (high); Hine (servant, peasant). The ending "G-r-r-r" confirms everything that has gone before.
How do these contribute to the theme? First, what is the theme of this malevolent diatribe? Looking at it from an internal perspective, the theme is that the speaker desires to trick Brother Lawrence into one of the "Twenty-nine distinct damnations" ennumerated in the New Testament Epistle of Galatians. Looking at it from an external perspective, the theme speaks of the error of jealousy, pride and hypocrisy. From the former, the speaker's theme is the damnation of Brother Lawrence, while from the latter the theme is the impending damnation of the poetic speaker. The sound affects work with both these themes to very soundly and roundly make and illustrate their points.