The next thing to do is run it in gear with all four wheels jacked up to see if you can duplicate the noise. If there's no noise, suspect a wheel bearing assembly. If the noise is still there, look underneath to see what is bouncing, binding, or jumping around.
On vehicles with universal joints at the wheels you would have noticed the slop or the binding when you removed the old shaft. On yours with cv joints, slop and binding are much less common, and it can be hard to detect when they aren't under load. Also, the chances of getting a replacement with exactly the same problem is pretty remote.
Also look at the brake calipers to see if one is moving sideways as the wheel turns. That would be a sign of a warped brake rotor, and grooves worn into the caliper mount can cause the pads' backing plates to catch as they move back and forth over them. That problem is worse when braking.
Ford products are also well-known for worn and sloppy ball joints. Look for one that is allowing the spindle to move around and let the cv joint or shaft hit something as it rotates. Look for anything that has shiny spots or scratches indicating it was rubbing. To find these things while running it jacked up you may need to place the front jack stands under the lower control arms to place the suspension in the same orientation as when the truck is sitting on the wheels, then try it again with the front jack stands under the frame rails which allows the suspension to hang down.
Look for unusual tire wear patterns on the front too. Smooth excessive wear on one edge of one tire points to a "camber" problem meaning the tire is tipped in or out on top. That could be the result of a worn ball joint. A feather edge on both tires indicates a "total toe" problem. That's related to something that changed the relationship of the steering linkages to the rest of the suspension system.
If you still haven't figured it out, have the steering and suspension systems inspected at a tire and alignment shop. Problems related to these systems should never be ignored on any vehicle, but Fords products have more than their share of part failures leading to crashes.
Sunday, September 16th, 2012 AT 8:39 PM