Barry -- Ordinarily I wouldn't correct a poster's punctuation, but since it's in your tag line you use for all your posts, it should be "isn't", not "is'nt", as in "If it isn't a Nikon..." Hope you accept that in good spirit as it was intended.
You may have sent an Alert to the Help Desk saying that you see an ERR. This is usually caused by the camera not making full contact or no contact at all with the lens. Make sure the lens is locked at its maximum aperture. If that doesn't work then the contacts on the camera and/or lens may need cleaning.
They all do that, dating back to my vintage-1977 F2A. It's a property of the design of the aperture stop-down mechanism. Since you have no lens in place, it rattles just a little bit. It's nothing to worry about.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!