What causes aircraft to swerve during takeoff? I notice on some commercial flights that the aircraft can begin to swerve left-to-right during takeoff before we leave the ground. Sometimes this can become very exaggerated, very hard left-to-right swerving. This is typically from around mid-way through the takeoff run, becoming most severe immediately before takeoff.

My first thought was perhaps it is an inconsistency in the runway from the airport I frequent but have noticed it once or twice at other airports as well, and across different carriers. However, it feels more like when driving a car and you swerve, then overcompensate the other direction and it becomes a vicious cycle. 

Other factors may include wind - but I've been in high-wind takeoffs before and it didn't have the same jerking motion. 

Any explanation to this, or am I just paranoid?



*Apologies for lack of knowledge re: terminology
I know you said that you don't think it's a crosswind, but honestly it most likely is.  As the plane speeds up and the wings start to generate more and more lift the plane is more easily affected by cross wind.  So, as you speed up, it gets harder and harder to keep the plane straight.  Throw in some gusts, and you're going to get some jerking motions as well.  Especially if that gust decreases the lift of the aircraft, the wheels suddenly catch the ground more and the craft is suddenly tugged harder than the pilot anticipated...

Here's a video of a Boeing 777 taking off in a heavy crosswind that should illustrate the point more.