Shutter Unstable In D90

[Polanski]

I've seen a lot of videos shot with D90. I don't know if it's only me or I sense some kind of opening and closing of the shutter. The image exposition is not stable. Are this guys using the camera in AUTO instead of MANUAL or is it another problem with the D90?

I think next year will be full of surprises with this new introduction of photo cameras with the capability to shoot HD video... I'd better wait...