Be silent now about member's trouble (6,5)
I believe the answer is:
tennis elbow
'member's trouble' is the definition.
(problem affecting a member)
'be silent now about' is the wordplay.
'about' indicates an anagram.
'be'+'silent'+'now'='besilentnow'
'besilentnow' is an anagram of 'TENNIS-ELBOW'.
(Other definitions for tennis elbow that I've seen before include "Muscular injury from exercise" , "Painful condition" , "Complaint in arm joint" , "Inflammation of an arm tendon" , "Tendon problem" .)