I have a 2004 f150 2x4 4.6 It has a vibration, feel like its in the rear, its noticed more when towing but sometimes it does it when I'm not towing. it comes and goes in waves not a constant vibration. its felt more in the seat than anywhere. tires have been changed any suggestions

 

Your rear tires may be out of balance.

 

I changed tires because I thought they were bad from factory but it still does it the new tire were balanced it shouldn't be the cause

 

how long ago did you change tires? maybe a weight fell off or maybe air pressure is off. how many miles on your truck? are the lug nuts tightened good ?

 

Possibility that its a u-joint tying up. If your handy, you should be able to drop it in 15-20 minutes (or less) and move the u-joint to see if its siezing or if its sloppy.

 

I had the same problem, dealer said change the tires, I did and no change. They ended up putting new rear rotors and 1 caliper all under warranty...problem fixed.

 

Make sure your parking brake is not hanging up. That was the source of mine. Did the vibration occur suddenly? Have you noticed this since you used your parking brake? Just one more thing to check.