From my experience, there are two drastically different levels of noise involved. My current D800 does make a rattle if you shake it, but it's very minor and I don't even think about it.
But, my first D800 sounded like something was broken in it. Just gently tipping the camera created a loud sound like something was rolling around in the flash housing. While this is not a problem for still photography, it was a real problem for video, since it was picked up easily and amplified by the internal mic. I sent that one back, and the replacement has a "normal" level of noise, which as I said, is not a problem for video.
If this is a new purchase, and you have a chance to return or exchange it, I suggest you get your hands on another D800/E body for comparison. If they both sound the same, then what you are hearing is probably the norm, and you'll quickly forget about it.
But if yours is much louder, then you probably have the same probliem I did with my first one, and I would exchange it for a new one while you have that option. Or, you can send it to Nikon for repair under warranty. The D800/E is an excellent camera, and I know you want to feel good about your investment. I understand how annoying that first sound was, even if you don't shoot video. Replacing my first one was a hassle, but I am glad I did.