If you have ever been in a wreck, or run over something big... the frame of your car could be touching something related to the engine, that shakes. I ran over a sewer cap that was too high off the ground once, and it jammed the front frame on the underside of my car back into my radiator, then into my enging mount, of my Camry. My car shook a TON! 4 Grand to get it all fixed.