I will preface this by saying that it is not a scholarly assertion nor the result of proven research. I do not intend to present a full academic proof, but rather to present a speculative theory which is open to refutation.
It is often stated that the most probable progenitor of the House of Hapsburg was a certain Guntramnus Dives (Guntram the Rich), perhaps identical to the third son of Hugh Count of Nordgau, of the Etichonid dynasty (the descendants of St. Adalrich of Alsace). This is based on the account of Acta Murensia written around the year 1160, stating that Lanzelin Count of Klettgau was the son of Guntramnus. There are however several problems with reconciling this account with the traditions of Hapsburg origin, particularly the traditional consensus of Carolingian descendant, and the possession of Klettgau. Yet what if the genealogy could be traced not to Guntram but directly to the Carolingians?