An Etymological Dictionary of the German Language/röcheln
röcheln, vb., ‘to rattle,’ from MidHG. rücheln, rüheln, ‘to neigh, roar, rattle’; allied to OHG. rohôn, MidHG. rohen, ‘to grunt, roar’; comp. Du. rogchelen, ‘to spit out.’ The Teut. root ruh, ruhh, preserved in these words, has been connected with the Slav. root ryk (from rûk); comp. OSlov. rykati, ryknąti, ‘to roar’ (Lett. ŕūkt), to which has to be added perhaps the Gr.-Lat. root rug in rugire, ‘to roar,’ ὀρυγμός, ‘roaring.’