klingen does not necessarily take the dative. The background is more general:
Verbs of sensing (like "klingen, sehen, hören, riechen") take the dative for the recepient of the sensing.
Die Schritte klingen ihnen zu einsam
Das Kleid sieht mir aber teuer aus
Der Ausflug hörte sich ihm zu gefährlich an
Das roch ihnen zu stark nach Betrug
This is BTW the same in English:
This sounded too lonely to him
The "zu" (or "to") is not needed (or rather: wrong) in German, because there is still an alive dative in this language, while English needs a preposition ("to") to signal this case.
This is one of the fundamental differences between the two Germanic languages English and German: English mainly drives relationships by prepositions, German by cases (and prepositions).