I recently purchased a 2006 FX4 as a replacement for my aging Expedition. It seems to shift hard every once in a while if I accelerate very slowly at speed. But, the bigger issue I think is that I noticed a very loud rattle that became very apparent while I was towing my toy hauler. It would stay constant while at speed and would go away immediately if I let off the accelerator. I thought it was only while pulling the trailer, but now I've noticed it a cruising speed even without the trailer behind me. It is much more difficult to hear, it becomes more apparent if I'm driving next to a wall or bigger vehicle in the right spot. Today I drove to work without the radio on and thought I could actually hear it through the firewall. Here I thought it was coming from the rear and today I find out it is either right below me or just on the other side of the fire wall. Any ideas on this?