The clatter does prove disconcerting (6)

I believe the answer is:

rattle

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'the clatter' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

(Other definitions for rattle that I've seen before include "led to Tweedledum and Tweedledees quarrel?" , "Infant's toy" , "Child's toy or kind of snake" , "making one upset" , "Child's toy; unsettle" .)

I've seen this clue in the Evening Standard.

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