What noise does it make when you chew an elastic band?

The bloke who shares my office has been making strange crunching noises since he moved in. Since I can’t see what he’s doing from behind my computer, I assumed he was a fan of eating rice crackers or popcorn or something. But all day? I finally asked what he was eating. Turns out he is actually chewing an elastic band, as a concentration aid. Never heard that one before. He tells me it used to drive his previous room–mate up the wall. No shit.