Soundest rhymes with:
blondest, fondest, grandest, kindest, propagandist, blondest, buddhist, coldest, eldest, encyclopedist, fondest, grandest, hardest, kindest, loudest, methodist, mildest, modest, oddest, oldest, orthopedist, prejudiced, propagandist, proudest, rudest, saddest, sadist, shrewdest, stupidest, weirdest, widest
Soundest sounds like:
sandquist, sandwiched, sanitized, santagata, scientist, smoothest, smudged, snatched, sundquist, syndicate, syndicated, synthesized