Healthy noise (5)
I believe the answer is:
sound
This clue is a double definition.
'healthy' is the first definition.
(I know that healthy can be written as sound)
'noise' is the second definition.
(I know that noise is a kind of sound)
(Other definitions for sound that I've seen before include "Fit" , "Valid" , "Reliable - noise" , "Safe" , "note, for instance" .)