system
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human
ELI5:What causes car engines to increase in noise and vibration over time?

New cars are usually silent with little vibration. Over time they become shaky and audible. Why? Is there a way to return them back to what they were?
gpt
Part of why it seems that way is because cars are always getting smoother and quieter. If you bought a new car 10 years ago, it would seem much quieter than an old car at the time, but it was louder than a new car today. The other part is mostly due to breakdown of noise insulating materials (both on the engine, and in the exhaust), and worn down motor mounts. Noticeable vibration in most older cars (assuming the engine is in good shape) is usually caused by bad motor mounts. One other thing is that engines lose compression, and therefore power, as they get older. This usually doesn't happen in every cylinder evenly. Some cylinders will wear more, and some less. This difference in compression will cause a difference in power output in each cylinder, causing vibration. This really shouldn't show up in a relatively modern engine until at least 150k miles or so.