Perhaps one is sound (5)
I believe the answer is:
noise
'sound' is the definition.
(a noise is a sound)
'perhaps one is' is the wordplay.
'perhaps' is an anagram indicator.
'one'+'is'='oneis'
'oneis' is an anagram of 'NOISE'.
(Other definitions for noise that I've seen before include "Clamour" , "Unwanted sound" , "Loud sound; bruit" , "explosive report, for example" , "interference" .)