Knock style of music (3)
I believe the answer is:
rap
I believe this is a double definition.
'knock' is the first definition.
('rap' can be a synonym of 'knock')
'style of music' is the second definition.
(I've seen this before)
(Other definitions for rap that I've seen before include "Small amount" , "Criminal charge" , "Urban music style" , "Form of music with chanted rhyming lyrics" , "Sort of music" .)