Siefert's rhymes with:
comforts, effertz, efforts, frankfort's, frankfurt's, lefferts, albert's, alberts, comforts, concerts, converts, deserts, eberts, eckardt's, eckert's, effertz, efforts, egberts, evarts, everts, expert's, experts, experts', filbert's, filberts, folkerts, frankfort's, frankfurt's, gaubert's, gewirtz, gilbert's, gizbert's, harberts, harcourt's, herbert's, hubert's, hulbert's, lambert's, lefferts, leubert, liverworts, mcroberts, megahertz, perverts, rewerts, robert's, roberts, roberts', schubert's, stalwarts, stewart's, stuart's, stuarts, taggart's
Siefert's sounds like:
sabertech, sabortech, sabretech, schubert's, seaports, separates, sephardic, shepard's, shepherd's, shepherds, sheppard's, sheppards, shipyard's, shipyards, spartacus, spartech, spartz, spirit's, spirits, sporadic, sport's, sports, sports', spreads, sprouts, spurts, subverts, supports