What could cause a vibration while driving down the motorway?

[TJwheeler]

What could cause a vibration while driving down the motorway?

 

[Mike Jones]

Worn out uni joints can do it

 

[TRDTom]

Wheels being out of balance?

 

[Harry May]

Flat spots in tires mate

 

[Sean Elias]

I was thinking the same thing, the wheel being unbalanced. But then again, it could be any of the above mentioned.