Number one's direction is sound (5)

I believe the answer is:

noise

'is sound' is the definition.
(a noise is a sound)

'number one's direction' is the wordplay.
'number' becomes 'no' (abbreviation).
'one's' becomes 'I's' (Roman numeral).
'direction' becomes 'e' (E is an example).
'no'+'is'+'e'='NOISE'

(Other definitions for noise that I've seen before include "Clatter" , "Uproar" , "Hum" , "Clamour" , "Sound - gossip" .)

I've seen this clue in The Telegraph and The Globe and Mail.

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