The most raucous is its one change (8)
I believe the answer is:
noisiest
'the most raucous' is the definition.
(I've seen this in another clue)
'is its one change' is the wordplay.
'change' indicates anagramming the letters.
'is'+'its'+'one'='isitsone'
'isitsone' anagrammed gives 'NOISIEST'.
(Other definitions for noisiest that I've seen before include "Making the loudest sounds" , "Biggest racket" , "party being at this extreme?" , "Making the most loud sounds" , "Most rowdy" .)