Are not quiet when healthy (5)
I believe the answer is:
sound
'healthy' is the definition.
(similar in meaning)
'are not quiet' is the wordplay.
I cannot really see how this works, but
'not' could be 'un' (I've seen this in other clues) and 'un' is found in the answer.
The remaining letters 'sod' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'when' acts as a link.
Can you help me to learn more?
(Other definitions for sound that I've seen before include "note, for instance" , "Measure depth" , "Safe" , "Fit" , "Ocean inlet or deep bay" .)