Stinking initials B.O. elicit sound of disapproval (10)

I believe the answer is:

sibilation

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'sound of disapproval' is the definition.
The definition suggests an adjective which matches the answer.

'stinking initials b o elicit' is the wordplay.
'initials b o' anagrams to 'SIBILATION'.
But, I'm not clear how the anagram is indicated.

Can you help me to learn more?

I've seen this clue in The Guardian.

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