The whole car shakes violently at anywhere between 1000-1500 RPM's. No matter what gear it's in. Up until a few weeks ago it's made a loud thunk! noise from the front of the car whenever you stop at a light or sign. Basically whenever there was a signifigant weight shift. Been doing that for a month or two. Now it stopped and the whole car just vibrates. Took it to a shop and they put the sensors in the exhaust and said the emmissions showed no problems. So it's apparently not a vacuum leak or timing or air/fuel problem. I'm thinking motor mounts. Thoughts? I did the test where you put the car through the different gears and gas it with the brake on to see if the engine moves a lot. It seemed to buck more in drive than reverse but I really don't know what's normal movement vs. what's excessive.