Couple turning noisy, left out (3)

I believe the answer is:

duo

'couple' is the definition.
(synonyms)

I cannot understand how the rest of the clue works.

(Other definitions for duo that I've seen before include "Two-person act" , "Performing pair" , "A team of two" , "They might play" , "Double act" .)

I've seen this clue in The Times.

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