I realize this may be a bit off the topic of long range hunting, but I do use this rig to hunt, so there is a connection and I have a feeling there's a few guys hanging out here that might have some ideas if they are willing to take a stab at it. Len, delete this if it's out of line. I've got a 1997 Explorer 4WD with a harmonic vibration that starts at 65mph and goes up as far as I've taken it. Typically at hwy speedds, it lasts for about 5 seconds then goes away for 3-4 seconds, then comes back in that cyclical fashion. I can feel it in the seat and some in the steering wheel, but I think that's (steering wheel) just because it's strong enough to feel it in the entire car. I did not recall noticing this until I purchased new Toyo Open Country 6 ply A/T tires last fall after blowing one of the same tires (about at the end of their life) on a trip that entailed 200 miles of nasty gravel roads on northern Vancouver Island. There were just a few feet on the aluminum rim til I stopped. Les Schwab has checked and double checked the rims alone. The other day (their suggestion, not mine) they gave me a complete set of new tires as they had found a little treadwell seperation in on the year old tires and the vibration was less, but still there. I recently had the upper control arms replace and had a new C/V joint replaced. Front sway bar bushings are just about 2 years old. 2 garages say there is nothing wrong with the front end or wheel bearings etc. Lower ball joints are new 2-3 years ago. It's been aligned 3x over the past year. This happens at a certain speed (65mph and above) over the ground so it's got to be txfer case output shaft or back from that. Local Ford garage said that the txfer case output shaft is good and tight. U-joints all check out good. Driveshaft out of balance? Something in the rear diff?