Racket is one problem (5)
I believe the answer is:
noise
'racket' is the definition.
(racket can mean a loud noise)
'is one problem' is the wordplay.
'problem' is an anagram indicator.
'is'+'one'='isone'
'isone' is an anagram of 'NOISE'.
(Other definitions for noise that I've seen before include "Fuss" , "Hubbub" , "Virgil's birthplace" , "Unwanted sounds" , "Confused sounds" .)