Why? The Hyundai diesel is one of the smoothest, quietest diesels around. They spent millions of dollars designing composite material oil pans, noise attenuators, they even have one of these magic mass dampers on the front engine mount. What noise are you trying to dampen? Vibration damping is a science, by randomly bolting on more mass you could end up exciting another vibration frequency that's worse. Tell us what noise you're trying to dampen it may be something others have already worked through.