Why do gerbils scratch at night?

You probably have a cage set-up where there isn't anyway that they can burrow, which is what they love to do. You could either A) ignore it, B) If you have a Critter Trail cage, you could purchase a cage extension called the Super Pet Critter Trail Burrowing Maze Accessory that you connect with an accessory tube from their main cage, to it, for them to burrow through, or C) Look through cage set-ups and make up one of your own. If you have an aquarium set-up to begin with, you can simply add a heavy deal of aspen wood shavings to the bottom of the cage where they will burrow through and make their homes.