Strings drop quietly within it, the movement (9)
I believe the answer is:
spaghetti
'strings' is the definition.
(I have seen 'Strings of pastas ' mean 'spaghetti' so perhaps 'strings' could also mean 'spaghetti')
'drop quietly within it the movement' is the wordplay.
'drop' becomes 'sag' (sagging is a kind of dropping).
'quietly' becomes 'p' (musical symbol).
'within' indicates putting letters inside.
'movement' is an anagram indicator (letters move around).
'sag' enclosing 'p' is 'spag'.
'it'+'the'='itthe'
'itthe' anagrammed gives 'hetti'.
'spag'+'hetti'='SPAGHETTI'
(Other definitions for spaghetti that I've seen before include "Birmingham interchange" , "Stringy pasta" , "It's past eight, time for strange pasta" , "meal" , "Strings of pastas" .)