Puzzles, from what we hear, producing agony (6)
I believe the answer is:
throes
'agony' is the definition.
(throes is a kind of agony)
'puzzles from what we hear' is the wordplay.
'puzzles' becomes 'throws' ('throw' can be a synonym of 'puzzle').
'from what we hear' indicates a 'sounds like' (homophone) clue.
'throws' sounds like 'THROES'.
'producing' is the link.
(Other definitions for throes that I've seen before include "Violent pangs of suffering" , "Anguish" , "Severe pangs of others" , "Pangs (at birth or death)" , "Pain pangs for others" .)