Paul occasionally interrupts loud argument in high-pitched voice (8)
I believe the answer is:
falsetto
'high-pitched voice' is the definition.
(I've seen this before)
'paul occasionally interrupts loud argument' is the wordplay.
'occasionally' means one should take alternating letters.
'interrupts' indicates putting letters inside.
'loud' becomes 'f' (short for forte - 'loud' in music).
'argument' becomes 'set to' (I've seen this before).
The alternate letters of 'paul' are 'al'.
'f'+'setto'='fsetto'
'al' placed inside 'fsetto' is 'FALSETTO'.
'in' acts as a link.
(Other definitions for falsetto that I've seen before include "Unusually high voice" , "High-pitched male voice" , "Extra high male singing voice" , "Aritifical upper register of male voice" , "Way of singing at higher pitch" .)