Sound of American serving in bar (7)
I believe the answer is:
logical
'sound' is the definition.
(I've seen this before)
'american serving in bar' is the wordplay.
'american serving' becomes 'gi' (GI is a term for a US soldier).
'in' is an insertion indicator.
'bar' becomes 'local' (I've seen this before).
'gi' going inside 'local' is 'LOGICAL'.
'of' is the link.
(Other definitions for logical that I've seen before include "Well thought out" , "Well-reasoned" , "having good reason" , "clear" , "Objective" .)