What causes an airplane to rhythmically bounce during taxiing? Some time ago, I was on a commercial flight and while the airplane was taxiing around, there was this rhythmic bouncing. Here is a video I made of the takeoff. You can notice the bouncing at the taxi and takeoff roll of the video. What causes that rhythmic bouncing? Is it a result of uneven wear on the tires?

For the sake of anyone who wants to know in case it helps, the airplane was a Boeing 757-200.
If you are old enough to remember, the bias-ply automobile tires used in the 1960's would develop a flat spot when left sitting overnight. The flat spot would quickly go away when you started driving. 

Many of today's aircraft tires still use bias-ply tires and are also subject to flat spotting. 



Source: The Boeing 737 Technical Guide