Rumble from ocean was disturbing to the ear (3,7)
I believe the answer is:
see through
'rumble' is the definition.
(both can mean to realise the truth about someone)
'ocean was disturbing to the ear' is the wordplay.
'ocean' becomes 'see' (I am not sure about this - if you are sure you should believe this answer much more).
'was disturbing' becomes 'threw' (to throw is to disturb or unsettle).
'to the ear' indicates a 'sounds like' (homophone) clue.
'threw' is a homophone of 'through'.
'see'+'through'='SEE-THROUGH'
'from' acts as a link.
(Other definitions for see through that I've seen before include "Rumble" , "Stay to the end" , "thin clothes" , "Transparent" , "help in time of need" .)