Here is the sentence:
Ernie is too noisy as a seatmate. Crunching on
apple slices, slurping hot coffee,
and the rings of his notebook snapped open and
shut all contribute to the cacophony.
When you list grammatical items, you must use parallel structure. Here, crunching on apple slices and slurping hot coffee are both gerund phrases, but the rings of his notebook snapped open and shut ruins the parallelism of the list. Good answer!
To fix the sentence, change the rings of his notebook snapped open and shut to snapping the rings of his notebook.