Break up 100 with a rolling sound (7)
I believe the answer is:
crumble
'break up' is the definition.
(I've seen this in another clue)
'100 with a rolling sound' is the wordplay.
I cannot quite see how this works, but
'100' could be 'c' (Roman numeral) and 'c' is found in the answer.
'sound' could be 'rumble' (rumble is a kind of sound) and 'rumble' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for crumble that I've seen before include "Break down, fall apart" , "(To) fragment; pudding" , "Break into small fragments" , "Break up - pudding" , "Type of pudding - disintegrate" .)