I usually can't hear, nor do I imagine, but I'm pretty sure when its happening because my parents suddenly decide to lock the door to their room (at 12AM? hmmm....) which makes a loud clicking noise.
For all you know, they might just like making peanut butter and jelly sandwiches in the dark.
Unlikely. Its pretty obvious when they're doing that, my dad chews like a beast.
Perhaps they are playing Monopoly and do not want to be disturbed.