Fundamentally, rock and roll comprises nothing but loud noise (4)
I believe the answer is:
roar
'loud noise' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for roar that I've seen before include "Cry (as a lion)" , "Lion's cry" , "Jaguar, for example, emits this" , "Bawl, bellow" , "Bellow, holler" .)