[zainsul]

When I shake my Lumia 930, there is a rattling sound coming from the camera.

When I open Nokia Camera, it becomes louder in photo mode.

It completely stops in video mode, only to return when i close the camera app.

PS: It does NOT come from the buttons on the side of the phone.

Is this normal?

[Racing Snake]

what you are hearing (I suspect), is the vibration motor.
The fact it 'disappears' when you open the video is pure coincidental, and suspect if you shook the phone a different way, or listened carefully it'll still rattle.
The apps (other than 'vibrating' when you open them) will have no effect on the rattle.

(is my guess)