querulous

habitually complaining

Given to quarreling; quarrelsome.

Latin 'querulus' meaning complaining

“In a fit of unjustified doubt of her sincerity, he complained, with a querulous snap: 'You have your own ideas; you have your own ideas.”

— George Meredith, Complete Project Gutenberg Works of George Meredith

“They are joined by Toad, who persuades Mole and Rat to join him on a holiday in his new horse-drawn caravan, pulled by the querulous horse Alfred.”