Such a noise swamps this capital city (5)

I believe the answer is:

hanoi

I'm a little stuck... Click here to teach me more about this clue!

'city' is the definition.
(Hanoi is an example)

'such a noise swamps this capital' is the wordplay.
'HANOI' is hidden within the letters.
However, I am not sure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for hanoi that I've seen before include "Asian capital on the Red River" , "Asian city" , "foreign city" , "Capital city of Vietnam" , "Vietnamese capital" .)

I've seen this clue in The Times.

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