Governor's wife in state to check in to ease sound (9)
I believe the answer is:
vicereine
'governor's wife' is the definition.
(I've seen this before)
'state to check in to ease sound' is the wordplay.
'state' becomes 'vic' (abbreviation for Victoria, Australian state).
'to' means one lot of letters go next to another.
'check' becomes 'rein' (both can mean to control or limit).
'in' indicates putting letters inside.
'to ease sound' becomes 'ee' (sounds like the plural of 'e').
'rein' put into 'ee' is 'ereine'.
'vic'+'ereine'='VICEREINE'
'in' is the link.
(Other definitions for vicereine that I've seen before include "Female provincial governor" , "governor's wife" .)