Mechanical device that could make one chatter (7)
I believe the answer is:
ratchet
'mechanical device' is the definition.
(I know that ratchet is a type of mechanical device)
'could make one chatter' is the wordplay.
'could make' indicates anagramming the letters.
'chatter' with letters rearranged gives 'RATCHET'.
'that' acts as a link.
(Other definitions for ratchet that I've seen before include "Chatter about notch on wheel" , "Chatter (anag)" , "Device promoting One Direction" , "One-way mechanism" , "Toothed device allowing unidirectional movement" .)