Engine mount troubles often cause noises from inside the car, including dashboard noise. So it's easier to start at the source. Hard connections between the engine and the body are often to blame....could be a cable, a hose, maybe a large wire harness.
So....if you can find a particular rattle inside the cabin, it's possible to fix or mute the noise. But you may also fix the noise at it's source under the hood. It's possible to fix most rattles....but sometimes not easy. I've used electronic "chassis ears" with multiple movable sensors, and a switch panel with earphones from the driver position. You'd drive around, and locate the sensor that picked up the noise. Then move the sensor around that particular area. Eventually you could isolate the noise.
There are cheaper versions of "chassis ears" using a single sensor. They work about the same as the version with many sensors....just take longer to find the problem. They can also be used to find suspension noises, but you have to be careful with the sensor wiring. I've seen such a device at Harbor Freight fairly cheap.
You can also ignore noise, or crank up the sound system. I usually try to find the noise. Dangerous engine noises can be mistaken for simple rattles if you're not careful....