Me too, I am having what seems to be the same problem. Only seem to feel the vibrating/hear the noise when the car has alot of weight in it, like a full car. Took it to one muffler shop and showed him what I thought was causing the problem, but he insisted that when the suspension moves, so does the rest of the car. Tried to get him to cut off my resonsators, but he refused, because he said it was illegal, like he was going to be paying the ticket if I were to get one.