i have a 2003 f150 supercab. i notice at high speeds it has a vibration to it. it's pretty pronounced. in fact, it will rattle any mettle in the cupholders loudly. it feels like my right rear is out of balance. i figure my crappy generals have something to do with it.

P.S. it it hardly noticeable at city speeds.

 

Have you checked to see if the tires are out of balance or if a rim is bent?

 

Do you feel the rattle in the steering wheel? I would suggest the same should be checked...bent rim and balance all four tires.

Something to keep in mind:

If you can feel the vibration/rattle in the steering wheel...then usually tires.

If you can feel the vibration/rattle in the seat of your pants...then usually powertrain. Like u-joints, bearings, etc.

Good luck with it.