Most clamorous one interrupting most prying (8)
I believe the answer is:
noisiest
'most clamorous' is the definition.
('noisy' can be similar in meaning to 'clamorous')
'one interrupting most prying' is the wordplay.
'one' becomes 'I' (Roman numeral).
'interrupting' is an insertion indicator.
'most prying' becomes 'nosiest' ('nosy' can be a synonym of 'prying').
'i' put within 'nosiest' is 'NOISIEST'.
(Other definitions for noisiest that I've seen before include "Making the loudest sounds" , "Biggest racket" , "Most rowdy" , "party being at this extreme?" , "Making the most loud sounds" .)