Rap artist thanks junk (3-1-3)
I believe the answer is:
rat-a-tat
'rap' is the definition.
(I have seen 'Sharp rap' mean 'rat a tat' so perhaps 'rap' could also mean 'rat a tat')
'artist thanks junk' is the wordplay.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'thanks' becomes 'ta' (UK informal version of 'thank you').
'junk' becomes 'tat' (both can mean rubbish).
'ra'+'ta'+'tat'='RAT-A-TAT'
(Other definitions for rat-a-tat that I've seen before include "Rapping sound" , "Noise of knocking" , "Knocking sound" .)