Nikon D5100 Video High Noise?

Just bought a nikon d5000 video (1080p) was crisp and so clear at first but about a week or two later I'm noticing a lot of noise in the video. Is something actually wrong with my camera? Or am I just not setting up lighting correctly and it's too dark?

The darker the room, the more the camera will compensate by raising the ISO.

higher ISO= noisier pictures. If you go out on a sunny day and record someone running, that footage should be crisp, clear, with very little to no noise to speak of