Bike wobbles with no hands: Why?

Where was the wobble coming from, front or back...?
Could be a dink or slight bend in your seat stay if you've took a tumble recently, either that or maybe your headset needs a tweek.

The wobble was from the front and identical to the first video above. There's nothing wrong with the bike which is a quality make full carbon fibre framed machine under a year old. The wheels flex slightly from side to side but then they do on my other bikes. Everything else is as new. The 'science' in the Sheldon (Jobst Brandt) article explains the causes nicely.