The most common reason for a banging noise is poorly loaded laundry. When the load is unbalanced with most of the garments on one side, the centrifugal force causes the machine to rock back and forth, creating the banging sound. Open the washer to make it stop, and then redistribute the laundry, so there is an even amount on all sides of the tub.
Under the washing machine, you will find four feet that the machine sits on, so the machine's main cabinet doesn’t scuff the floor. They also keep the machine level. When these feet are not adjusted properly, the machine rocks back and forth with the slightest movement. When they are not level, the spin cycle causes the machine to whip back and forth very quickly, creating a bang as each of the off balance sides strikes the floor. You can easily adjust these feet by lifting the back of the machine off the floor. Repeating this with the front side. If your Roper model doesn’t have adjusting feet, turn them one way or the other to adjust the level.
The outer tub of your washing machine is kept in very delicate balance by internal parts in the washer. Depending on your model, your Roper or Whirlpool washer might use springs, pistons or counterweights to make it remain balanced during use. If any of these balancing mechanisms wear out, break or fail, the tub will shake and shimmy, causing banging noises that will have to be repaired before the washer can be properly used again.
Pay attention to the type of floor your washer is sitting on. The problem may not be the washer. The machine is quite heavy, and it is even heavier when filled with water. Unless your floor is supported by a concrete slab, then the vibration from the machine can cause the floor to shake. This vibration can make the washer jump up and down a bit, which accounts for the banging noise.