Making a certain sound when stealing away (10)

I believe the answer is:

aspirating

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'making a certain sound' is the definition.
I can't judge whether this definition defines the answer.

'when stealing away' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'stealing away' becomes 'pirating' (pirating is a kind of stealing. I am not sure about the 'away' bit.).
'as'+'pirating'='ASPIRATING'

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I've seen this clue in The Independent.

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