In a manner that makes loud, rattling, consecutive noises.
From clattering (present participle of clatter) plus -ly adverbial suffix, creating an adverb describing how something happens with clattering sounds.
Adverbs ending in -ingly are wonderfully expressive in English—they let us describe not just an action but how it sounds, feels, or appears, turning simple verbs into vivid sensory descriptions.
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