Sound expert the French follow (7)
I believe the answer is:
crackle
'sound' is the definition.
(I know that crackle is a type of rattle)
'expert the french follow' is the wordplay.
'expert' becomes 'crack' (as in 'a crack team').
'the french' becomes 'le' ('the' in French).
'follow' is a charade indicator (letters next to each other).
'crack'+'le'='CRACKLE'
(Other definitions for crackle that I've seen before include "Rustle loudly" , "sort of porcelain" , "Sound as of dry twigs burning" , "Noise as of burning twigs" , "Noise of, eg, electrical discharge" .)