Instrument is Spooner's orchestral nightmare (8)
I believe the answer is:
handbell
'instrument' is the definition.
(I know that handbell is a type of idiophone)
'is spooner's orchestral nightmare' is the wordplay.
I cannot really see how this works, but
'is' could be 'be' and 'be' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for handbell that I've seen before include "percussion instrument" , "Chiming instrument" , "Manual ringer" , "One of set used for ringing practice" .)