How to get noise free low lighting video with my nikon d5100?

I just find noise in most of my videos i take

Video normally doesn't like low lighting - the more light you have the better cos all the electronics are working in overdrive under low lighting.

Add light.

This should not be a surprise

Video and motion picture production companies always add light when shooting a scene that emulates "low light"

Here is a link to such a video. Lighting is one of the most important pieces when shooting video, film or a digital camera.

All the interior shots were shot using supplemental lighting that simulates that actual lighting found in the scenes

If you have ever visited a sound stage on a motion picture production company like Fox, Burbank Studios, Sony, Paramount, etc, you will see they use huge lights, including 1K and 2K lamps. Usually a few 250 watt, 500 watt and 750 watt lamps will do the job for your video productions. Remember that you will need some light modifiers to produce the controlled lighting necessary to get the lighting just what you want.

I'm guessing that the only lens you have is the slow, variable aperture 18-55mm f3.5-5.6 zoom that came with your camera. This lens is woefully inadequate for use in low-light/available light photography or videography.

I suggest investing in a couple of fast prime lenses such as the AF-S Nikkor 28mm f1.8G or the AF-S DX Nikkor 35mm f1.8G or the AF-S Nikkor 50mm f1.8G.No, these prime lenses don't zoom so you'll have to learn to "zoom" like we did before zoom lenses were invented - step closer to get less in the scene or step back to get more in the scene.

An f1.8 lens is a full 2 stops faster than your kit lens at 18mm and f3.5 and 3-1/3 stops faster than your kit lens at 55mm and f5.6. This means being able to use a lower ISO which means less of that bothersome digital noise you complained about. Suppose at 18mm and f3.5 an ISO of 3200 was needed to get a shutter speed of, say, 1/200 sec. Switch to one of the f1.8 primes and you can use ISO 800 to achieve the same shutter speed.

If you believe that you absolutely can't do the videos you want to do without a zoom lens then buy the AF-S DX Zoom-Nikkor 17-55mm f2.8G IF-ED. Its only 2/3 stop faster than f3.5 but its a full 2 stops faster than f5.6.

As someone suggested you could add light to the scene but buying adequate lighting will be as expensive - if not more expensive - than investing in fast prime lenses or the aforementioned fast zoom lens. Plus lights have to be lugged around with you and set up and then taken down.