Go down quietly — I had returned (3)
I believe the answer is:
dip
'go down' is the definition.
(I've seen this before)
'quietly i had returned' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'i had' becomes 'id' (I'd**).
'returned' is a reversal indicator.
'p'+'id'='pid'
'pid' in reverse letter order is 'DIP'.
(Other definitions for dip that I've seen before include "See 21" , "A quick bathe" , "Pickpocket" , "Lower into water for short swim" , "Slope downwards" .)