I have a 04 TB EXT 4x4 that has developed a 'rattle' above 45 MPH. It is more of a vibration in the floorboard than a noise and is only noticeable on a smooth road. The best description I can give is it feels like someone is hitting the floorboard with a rubber mallet intermittently. The frequency does not seem to be consistent or linked to RPM/MPH. I blew a seal on the front diff a couple of years ago and had that replaced. I checked all the U-joints for play and they seem fine. The car has 161K and has been fantastic other than a few minor issues.