...but not your normal out of balance tire or drive shaft vibration.

Just the other day my truck started making a random vibration from time to time. I have never felt anything like it ony any truck before. It feels/sounds like I am driving on rumble strips on the side of the road. It only does it for a couple seconds at a time and does not affect driveability. Visually everything looks good. Any ideas as to where to start?

 

If your truck is a quad cab you will have a two-piece drive shaft with a steady bearing. It sounds to me like the rubber support on the outside of the bearing could be worn out or even separated. Give your drive shaft a push from side to side and see how easily it moves in that bearing. Should stay centered without moving very much.