How can I stop my panda bear hamster from biting!?

Ok, I bought my panda bear hamster named Oreo early in the summer. However, as of the past two months she chews on the cage doors constantly so it twangs when my fiance and I are trying to sleep. I have tried everything to keep her entertained we bought a $100 dollar cage set up, which contains two different wheels, a hammock, and two observation decks. She just seems to be very board. We even went as far to buy her, her own play pen! in which she can be outside the cage in! Anyone have any advice? I love her dearly but she is driving my fiance completely bonkers at night.