Not for sure...bought the truck with 105k and didn't notice it then. About a month after I bought it, the front driveshaft u-joints were clicking and starting to move around a bunch so I had the front driveshaft rebuilt. With the front shaft off, it doesn't seem to vibrate as much or hardly at all...that's why I was sure it was the front driveshaft out of balance somehow but after having it balanced 3 times I figured they'd get it right.