Unexpected metal I see on the radio (6)
I believe the answer is:
ironic
'unexpected' is the definition.
(similar in meaning)
'metal i see on the radio' is the wordplay.
'metal' becomes 'iron' (iron is a kind of metal).
'on the radio' shows a homophone (sound like).
'see' sounds like 'c'.
'iron'+'i'+'c'='IRONIC'
(Other definitions for ironic that I've seen before include "turning out unexpectedly" , "Describes a statement that says the opposite of what is clearly the case" , "rich" , "W. Country port, its Channel" , "not as you'd expect" .)