Perhaps mobile, with its case, producing little sound (7)
I believe the answer is:
phoneme
'little sound' is the definition.
'perhaps mobile with its' is the wordplay.
'perhaps mobile' becomes 'phone'.
'with' is a charade indicator (letters next to each other).
'its' becomes 'me' (I can't explain this - if you can you should believe this answer much more).
'phone'+'me'='PHONEME'
'case producing' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
(Other definitions for phoneme that I've seen before include "Small bit of speech" , "distinctive sound" , "Unit of spoken sound" , "minimal piece of speech" .)