Depressed squealer's country music (9)
I believe the answer is:
bluegrass
'country music' is the definition.
(bluegrass is a type of country music)
'depressed squealer's' is the wordplay.
'depressed' becomes 'blue' (I've seen this before).
'squealer' becomes 'grass' (both can mean an informant).
'blue'+'grass'='BLUEGRASS'
(Other definitions for bluegrass that I've seen before include "nickname of US State" , "Style of US country music" , "American hillbilly music" , "Style of country music from Kentucky" , "A type of country music" .)