Girl is quiet before noon (3)
I believe the answer is:
pam
'girl' is the definition.
(short for Pamela)
'quiet before noon' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'before noon' becomes 'AM' (as in AM on a clock).
'p'+'am'='PAM'
'is' is the link.
(Other definitions for pam that I've seen before include "- Ayres, English poet" , "Short girl's name" , "Female" .)