Fan opinion — sell-out sounds annoying (5,9)
I believe the answer is:
'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).
'opinionsellout' anagrammed gives 'NOISE POLLUTION'.
(Other definitions for noise pollution that I've seen before include "that's unwelcome to hear" , "Harmful din" .)