The sound of sales talk (6)
I believe the answer is:
patter
'talk' is the definition.
(I have seen 'Rapid talk ' mean 'patter' so perhaps 'talk' could also mean 'patter')
'the sound of sales' is the wordplay.
'the sound' becomes 'pat' (pat is a kind of sound).
'of sales' becomes 'ter' (I can't explain this - if you can you should give a lot more credence to this answer).
'pat'+'ter'='PATTER'
Can you help me to learn more?
(Other definitions for patter that I've seen before include "Salesman's chat - walk with quick, soft steps" , "idle talk" , "Noise of fast light steps" , "Comedian's, salesman's, talk" , "conjuror's monologue" .)