jud·der 
(jŭdər)
(jŭdər)intr.v. jud·dered, jud·der·ing, jud·ders
To shake rapidly or spasmodically; vibrate conspicuously: "Edith would watch her wrestling with words, her thin little body juddering with the effort to unlock them" (Anita Brookner).
n.
A rapid or spasmodic shaking.
[Perhaps J(ERK)1 + (SH)UDDER.]