An Etymological Dictionary of the German Language/Annotated/wispeln
wispeln, verb, ‘to whisper,’ from the equivalent Middle High German wispeln, Old High German wispalôn, hwispalôn. Also in Modern High German only, wispern (properly perhaps a Low German word), corresponding to Anglo-Saxon hwisprian, English to whisper. These intensive forms seem to be based on an onomatopoetic root hwī̆s (hais), to which also heiser is usually referred.