Mutter in agitation about parking for orchestra member (7)
I believe the answer is:
trumpet
'mutter' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for trumpet that I've seen before include "Brass wind instrument" , "Loudly sound - instrument" , "brassy type" , "Centre of daffodil flower" , "Orchestral or military instrument" .)