I have a 2003 F 350 long bed CC 6.0. I love this truck but I'm about to put some C4 to it and let it rest!

I have about 10K on some new Toyo tires and i have rotated them with no success.

Here is the problem, I have developed a rattle, vibration or hum when I hit about 50 mph and it gets worse the faster I go. The sound is a progressively increasing hum that turns into a rattle that starts from the passengers front wheel. IT sounds like it starts at the passengers side front wheel area and then moves to the front center of the truck. It is not in my steering, not in my brakes or under my seat. It starts at 50 mph and gets worse as I go faster. If I get up to 70 mph, It sounds like a single rock is attached to a string flying around the wheel well of my front passengers wheel well. If I slow down the rock type sound goes away, the hum continues till I drop below 50mph.

It is not RPM related. I've tried to reproduce this in a lower gear, similar RPM. Nothing! It's definitely speed related. When I hear of speed related vibrations, I think tires or brakes. I've checked my brakes, nothing abnormal and I can not feel this in the brakes or steering, only the front of the truck. As I said, I rotated tires with no resolution to the problem.

I have tried using my brakes during the hum/vibration and it has no effect on the problem. I feel no vibration or pulsing on the brakes.

I have removed the brake caliper and inspected the disc's and nothing looks abnormal at all! Both front and L and R sides.

I have jacked the truck up, did the 0900-0300 and 0600-1200 pulling to verify if there is any U-joint movement. NOTHING! hubs seem fine, and upon inspection of axle U-joints, everything is in place, no cracks, no problems of any concern that is visible. I have jacked the front of the truck up, locked the hubs and both wheels turn without catching, even when turning the steering wheel L to R. Not axle U joints. When I run the auto hubs in auto, the axles spin freely with no problems.

I get under the truck and start pulling on the front drive shaft. U joints have NO PLAY. One thing I did notice is that I can move the driveshaft at the black accordion area that is 1 foot from the pumpkin and it does make a subtle clunk but hardly moves.

I have rotated my tires with no resolution to the problem.
I removed the sway bar and sway bar links, no resolution to the problem.

I would appreciate any help or direction as i'm at my wit's end!