excessive noise is video shots are often caused by poor or low lighting conditions, so ultimately you may want to look at ways to improve the lighting in your shots.
but to help with you current footage, you can try the remove grain effect. this will produce a general softening of the image… if you only need to lessen the noise in certain areas of the footage, you can create mattes for those areas. this tutorial demonstrates a pretty useful way to matte out areas for remove grain and then add a bit of noise back into the shot… it’s probably worth looking at.
https://www.videocopilot.net/tutorials/blemish_removal/
also, if you footage is interlaced and you are rendering progressive, you can lessen noise by simply enabling frame blending (layer>frame blending>frame mix, not pixel motion). this will use the data from the other field and blend it with deinterlaced image and can help to reduce noise by about 50% with hardly any additional render time (remove grain is a big render hit).
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW