Soundness rhymes with:
blandness, blindness, fondness, kindness, sandness, awkwardness, backwardness, badness, baldness, blandness, blessedness, blindness, bloatedness, boldness, coldness, crookedness, discontentedness, fadness, farsightedness, fondness, goodness, handedness, hardness, high-spiritedness, kindness, lightheadedness, low-spiritedness, madness, mindedness, nearsightedness, poor-spiritedness, preparedness, public-spiritedness, redness, rudeness, sadness, sandness, shrewdness, spiritedness, vividness, weirdness, wickedness, wildness
Soundness sounds like:
sanding, sandino's, sandness, scantiness, sending, sentence, sentences, shandong, shantytowns, shunting, smeeting, smoothens, smoothing, smoothness, something, something's, somethings, sometimes, sondheim's, sounding, soundings, squinting, sumitomo's, summations, sundance