I have a 2002 trailblazer ....has had no major problems. But recently when slowing down and when at a stop the car vibrates. What could cause this? We recently tightened the bolts on the exhaust manifold and do not think it is the motor mounts but not 100 positive. Any suggestions? There is also a slight wobble feeling at highway speeds that started around the same time but not sure that it is connected.