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. :cool:
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.