i'm trying to produce a few mockup pictures of a person using a tablet around the house. These are the conditions:
- Camera Nikon D90, Lens 18-55
- The pictures were taken in the morning
- Indoors but the room has a lot of natural light
- I didn't use zoom, the 'subject' was around half meter away from the camera
- Shooting Mode 'A', Image quality is RAW Fine, ISO 200 - 2000, F5.6v
The result was not good, the pictures have a lot of noise and grain.

How can i take crystal clear pictures without grain?
Thank you