This musical instrument has upset neighbour (4)
I believe the answer is:
tuba
'this musical instrument' is the definition.
(tuba is a kind of musical instrument)
'upset neighbour' is the wordplay.
'upset' shows that the letters should be reversed in order.
'neighbour' becomes 'abut' (I've seen this before).
'abut' written backwards gives 'TUBA'.
'has' acts as a link.
(Other definitions for tuba that I've seen before include "Deep brass instrument" , "Brass band instrument" , "Producer of note" , "It's not top brass" , "member of band" .)