Cat grabs a radio's top sound producer (6)
I believe the answer is:
larynx
'sound producer' is the definition.
(the larynx is the voicebox)
'cat grabs a radio's top' is the wordplay.
'cat' becomes 'lynx' (lynx is a kind of cat).
'grabs' means one lot of letters goes inside another.
'top' indicates taking the first letters.
The first letter of 'radios' is 'r'.
'a'+'r'='ar'
'lynx' placed around 'ar' is 'LARYNX'.
(Other definitions for larynx that I've seen before include "Organ containing the vocal cords" , "box of cords?" , "Human voice box" , "part of throat with vocal chords" , "Upper part of the windpipe" .)