The Hinge Clacker appears to be a kind of tool, seen Master Payne's Circus of Adventure hits the road. Agatha thinks one would be useful for fixing Dame Aedith's wagon, which has started to make some strange noises -- or at least so she leads Dame Aedith to believe. In fact, while Dame Aedith is off looking for a hinge clacker (eventually finding one, probably in Rivet's huge stash of tools), Agatha "fixes" what's really making the noise in the wagon axle: the large group of Dingbots that have taken up residence there after they made repairs to the wagon, repairs that the Circus credits to Agatha. Agatha doesn't want her Dingbots made known to the Circus yet, so she quiets them down and returns them to hiding. It's fair to say that they'll come in handy later ..., as
She never does actually use the hinge clacker, but no matter.