Low frequency noise in recording decayed (8)
I believe the answer is:
crumbled
'low frequency noise' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?
'in recording decayed' is the wordplay.
'in' is an insertion indicator.
'recording' becomes 'CD' (type of recording).
'decayed' becomes 'rumble' (I can't justify this - if you can you should believe this answer much more).
'cd' placed around 'rumble' is 'CRUMBLED'.
Can you help me to learn more?
(Other definitions for crumbled that I've seen before include "fell apart" , "went to pieces" , "fragmented" .)