An Etymological Dictionary of the German Language/Annotated/röcheln
röcheln, verb, ‘to rattle,’ from Middle High German rücheln, rüheln, ‘to neigh, roar, rattle’; allied to Old High German rohôn, Middle High German rohen, ‘to grunt, roar’; compare Dutch rogchelen, ‘to spit out.’ The Teutonic root ruh, ruhh, preserved in these words, has been connected with the Slavonic root ryk (from rûk); compare Old Slovenian rykati, ryknąti, ‘to roar’ (Lettic ŕūkt), to which has to be added perhaps the Greek-Latin root rug in rugire, ‘to roar,’ ὀρυγμός, ‘roaring.’