Shaking in your car can range from barely noticeable to teeth-rattling. It can also start for multiple reasons. You may find that your car's shaking starts suddenly one day when you turn on the vehicle. You may even begin to notice that it feels shaky when you hit the brakes. As with any car problems, it's a good idea to have your car inspected thoroughly and properly by a mechanic. However, you can get a sense of what's happening with your vehicle based on its symptoms.