Constant Interior noise need help

Noise coming from this white thing under steering wheel, by the gas pedal, it keeps moving back and forth and just makes this annoying sound just like if u loose a pen in the air vent when you have air Blowing, at first I though it was a pen in the air vent but then looked down under and saw that thing moving and making noise.
Idk what that thing is for and what it keeps moving. Need help