One way to do that is to build them using metal composites such as Quiet Steel from Material Sciences Corp., Elk Grove Village, Ill. (www.matsci.com). It consists of metal outer skins sandwiching a 0.001-in.-thick layer of viscoelastic polymer. The material can be processed using standard metalworking techniques, including slitting, roll and brake forming, drawing, and punching. It can also be brazed, bonded with adhesives, and welded without using shunts or bypass circuits. The material is 100% recyclable and can be engineered to meet specific noise damping, temperature tolerance, stiffness, and environmental requirements. Quiet Steel has been used successfully in automobiles, appliances, air conditioners, office furniture, and hard-disk drives.