Was aware of modern sounds (4)
I believe the answer is:
knew
'was aware' is the definition.
(I've seen this before)
'modern sounds' is the wordplay.
'modern' becomes 'new' ('new' is associated in meaning with 'modern').
'sounds' shows a homophone (sound like).
'new' sounds like 'KNEW'.
'of' is the link.
(Other definitions for knew that I've seen before include "Distinguished" , "Was cognizant of" , "Was cognisant or aware of" , "Understood" , "Was conscious of" .)