I would crawl under the mid of the truck and check to see if the heat shield is vibrating against something.
Since it's consistant and speed related, a good bet would be that it is wind or RPM related. If is RPM related it's doubtful the vibration would make it's way to the seating area in the back without you being able to feel it up front also. But if it is RPM related it could be something under the truck resonating.
Maybe crawl under and (make sure the truck is cold) and lightly bang on the exhaust and see if you hear the rattle. Take your finger and "flick" the edge of the heat shield above the muffler and see if it rattles. Check your trim on the outside on the PS of the truck to make sure wind is not the culprit.
Somebody else might have some other thoughts.
|