Turns down rubbish song's intro (7)
I believe the answer is:
refuses
'turns down' is the definition.
('refuse' can be a synonym of 'turn down')
'rubbish song's intro' is the wordplay.
'rubbish' becomes 'refuse' (I've seen this before).
'song's intro' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'refuse'+'s'='REFUSES'
(Other definitions for refuses that I've seen before include "Says no" , "Declines" .)