A quarrels heard to stimulate ... (6)
I believe the answer is:
arouse
'to stimulate' is the definition.
(arousing is a kind of stimulating)
'a quarrels heard' is the wordplay.
'quarrels' becomes 'rows' ('row' can be a synonym of 'quarrel').
'heard' indicates a 'sounds like' (homophone) clue.
'rows' is a homophone of 'rouse'.
'a'+'rouse'='AROUSE'
(Other definitions for arouse that I've seen before include "Excite, awaken" , "Set off" , "Incite or stimulate" , "Ginger up" , "Excite; provoke" .)