A very loud voice causes concern (6)
I believe the answer is:
affair
'concern' is the definition.
(I know that affair is a type of concern)
'a very loud voice' is the wordplay.
'very loud' becomes 'ff' (musical abbreviation).
'voice' becomes 'air' (both can mean to express something).
'a'+'ff'+'air'='AFFAIR'
'causes' is the link.
(Other definitions for affair that I've seen before include "Matter or concern, perhaps of the heart" , "Secret romance" , "See 23" , "Liaison or intrigue" , "Thing to be done with raffia" .)