Fan opinion — sell-out sounds annoying (5,9)
I believe the answer is:
noise pollution
'sounds annoying' is the definition.
(noise pollution means annoying or disruptive noise)
'fan opinion sell-out' is the wordplay.
'fan' is an anagram indicator (letters must be fanned around).
'opinion'+'sell'+'out'='opinionsellout'
'opinionsellout' anagrammed gives 'NOISE POLLUTION'.
(Other definitions for noise pollution that I've seen before include "that's unwelcome to hear" , "Harmful din" .)