When I shift to drive or reverse there's a loud bang when shifting

Hello, Your motor mounts are likely the issue. They are insulated metal brackets, and when the rubber insulation wears out, cracks, leaks out the fluid (sounds funny I know), or dries out, they will not have enough stiffness to hold the engine when it wants to rock. Have the engine mounts inspected before buying the parts. If you want to see for yourself, have someone put on the parking brake, hold the brake pedal down as well, pop the hood, and watch the engine while they shift from reverse to drive. The engine will likely rock back and forth harshly.