item flickers when rendered

Hi I have started my little animation and have a stationery item in the background (a cardboard box) and when i rendered it one of the open flaps flickers when i change the camera position. I have tried looking at the normals but they are ok and cant see why it happens. It only happens on this one tiny little bit but it is really noticable when you watch the short animation. I have saved it as an AVI so dont know how to show you the result so you cvan see what i mean.

Any help or advice would be really appreciated. Its only my first pass so the animation is not exact as yet but want to solve the problem before i go on.

Many thanks

Ensure no overlapping faces or duplicate objects in the scene. Please supply example file

bang on worked like a charm thanks for the assistance