Nikon D7100?

Issue #1) This is the vibration reduction (VR) system. It is probably normal operation.

Issue #2) This is probably the len's VR. Turn VR off and the sounds/vibration will go away if it is indeed being caused by the VR system. If not, then take the lens back for an evaluation, repair or exchange.

You should clean the inside of the camera. Do so with caution to avoid damaging the mirror or shutter. Using a blower like a Giotto Hurricane Blower is a great tool for removing loose debris from the mirror box and from the surface of your sensor. A lite blowing out of the box is typically the only thing you'll ever need to do with the exception of cleaning the sensor itself.

When do you clean the sensor? You can easily check when it's time to clean the sensor by taking a photo of a white piece of paper with the lens out of focus. If the sensor is dirty with bits of dust, they'll show up easily on the white background as gray, fuzzy spots. Using white paper just makes it very easy to see the dust spots. If you do have dust on the sensor, using the Giotto blower is the first step. If that doesn't work, then you need to get a sensor cleaning kit like those sold by Visible Dust.

The mirror shouldn't be cleaned or touched unless you have some debris on it that can't be blown off with the Giotto blower. To clean the mirror, use lens cleaning solution only. Never use anything else other than lens cleaning solution. Put a few drops onto a micro fiber cleaning cloth and gently wipe the mirror. Never apply cleaning solution directly to the mirror. Always apply cleaning solution to the cloth.

Use the Giotto blower to remove any loose dirt and debris from the front/rear of your lenses.

If you were out taking photos in a dusty area, or the beach, be sure to clean off the lens and body before removing the lens to avoid any loose dirt and debris from entering the camera and possibly causing damage to the mirror, shutter or sensor.

Follow these steps, and with some common sense your camera will provide years of service.

The movement and clicking is causef by the image stabilisation aka vibration reduction in the lens.

Some lenses click and whirr and move the viewfinder image on stsrtup but it could also be a sign that your lens is about to die

Read Frank's reply again. I was about to suggest similarly. It seems to be a VR issue, unless it's the auto-sensor cleaning function going haywire. Does this happen with all lenses you use? Did you make certain the VR function is turned off? I suggest you take it to the camera brand company service shop to inspect/repair the problem, with their specialized, trained, experienced technicians. Do NOT try to clean it on your own; you can cause far more damage and harm than you can begin to realize, and make matters worse (and more costly to repair). Let the pros clean it (it's worth the price knowing it won't be damaged). Good luck and best wishes.

I very much doubt that cleaning is going to help. My first thought is that it's something to do with image stabilisation - have you tried a different lens?

It might be the auto sensor cleaning system or the vibration reduction going on but if you really are concerned about it, have your camera checked at the service center. Don't clean it yourself.

Nearly forgot... The camera has not fallen on the floor, did not sustain any knocks.