Sound hooter about one (5)
I believe the answer is:
noise
'sound' is the definition.
(a noise is a sound)
'hooter about one' is the wordplay.
'hooter' becomes 'nose' (informal term).
'about' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'nose' enclosing 'i' is 'NOISE'.
(Other definitions for noise that I've seen before include "Loud or disturbing sound" , "Din, cacophony" , "explosive report, for example" , "Unwanted sounds" , "Rumour" .)