Piped down, so we hear (4)
I believe the answer is:
blew
'piped' is the definition.
'down so we hear' is the wordplay.
'down' becomes 'blue' (I've seen this before).
'so we hear' indicates a 'sounds like' (homophone) clue.
'blue' sounds like 'BLEW'.
(Other definitions for blew that I've seen before include "Gusted" , "Puffed and panted" , "Breathed hard" , "Played (a horn)" , "Spent recklessly; exploded suddenly" .)