You'll have several levels of quiet operation to choose from. Your lifestyle and the proximity of your kitchen to family gathering areas will be a factor in your choice. If you have a lot of family activities and conversations taking place in or near the kitchen, you'll probably want a quieter dishwasher. The most important feature for sound reduction is the amount of insulation around the washing tub. Other features which reduce sound include insulation in the door, toe panel and access panels.
Some models even have very quiet motors and vibration-absorbing material linked to the motor.
The amount of energy you save is basically up to you. Just buying a dishwasher will probably reduce your energy costs. Many studies show that new dishwashers use less hot water and energy than washing by hand. And, if you don't prewash, you'll save even more. Another big factor in saving energy is your choice of wash cycle.