Ruling heard when it's pouring (7)
I believe the answer is:
raining
'it's pouring' is the definition.
(I've seen this before)
'ruling heard' is the wordplay.
'ruling' becomes 'reigning' (reigning is a kind of ruling).
'heard' indicates a 'sounds like' (homophone) clue.
'reigning' is a homophone of 'RAINING'.
'when' is the link.
(Other definitions for raining that I've seen before include "Falling in drops" , "With water falling from the sky" , "Depositing cats and dogs" , "Showery" , "Bad weather" .)