If you feel comfortable, it's often best to simply just ask the person or group to be a little quieter. Most people don't realize that they are being loud and will quiet down if asked. 

If you have already asked or feel uncomfortable asking, you can visit the Check Out Desk on the ground floor of the Sturgis Library (Kennesaw). If you're in the Johnson Library (Marietta) see the Check Out Desk on the first floor. A library staff member will be glad to ask the loud patron or group to quiet down.