Jar's good value (5)
I believe the answer is:
grate
'jar's' is the definition.
(make unpleasant sound)
'good value' is the wordplay.
'good' becomes 'g' (abbreviation).
'value' becomes 'rate' ('rate' can be a synonym of 'value').
'g'+'rate'='GRATE'
(Other definitions for grate that I've seen before include "Jar; fireplace" , "irritating" , "Rasp; fire holder" , "part of fireplace" , "Rasp; shred" .)