If this has only occurred once it is possible that the door wasn't fully closed.
If this was the case the door may have been making and breaking contact with the sensor in the door striker (#6 in the image below) as you rode over bumps, thus causing the window to chatter.
It is also possible that the door striker may need to be replaced due to damage.
If you take a good look at the door striker you will notice there is a push button (the sensor) located behind the cylinder portion. When the door makes contact with this push button the window is rolled up completing the seal.
When my window started doing this it turned out that the plastic push button was worn down preventing the door from making proper contact with the sensor. The part was $50 canadian from the dealership.