Prepared to listen: piece of music a horrible noise (5,2)
I believe the answer is:
tuned in
'prepared to listen' is the definition.
(tuned in to the radio)
'piece of music a horrible noise' is the wordplay.
'piece of music' becomes 'tune' (a tune is a piece of music).
'a horrible noise' becomes 'din' (a din is a noisy disturbance).
'tune'+'din'='TUNED IN'
(Other definitions for tuned in that I've seen before include "Prepared to hear" , "Adjusted radio set" .)