Joints on the end of guitar frets (7)
I believe the answer is:
rankles
'frets' is the definition.
('rankle' can be a synonym of 'fret')
'joints on the end of guitar' is the wordplay.
'joints' becomes 'ankles' (ankle is a kind of joint).
'on' says to put letters next to each other.
'the end of guitar' becomes 'r' (I can't justify this - if you can you should give a lot more credence to this answer).
'ankles' put after 'r' is 'RANKLES'.
Can you help me to learn more?
(Other definitions for rankles that I've seen before include "Goes on vexing" , "Continues to hurt" , "Riles" , "Causes lasting and bitter annoyance" .)