Not achieving smooth gradient in CS3

Question

Hi
I'm simply trying to set up a gradient in Photoshop CS3, which blends from left to right on an A4 page. The gradient at the left is 15 per cent of Pantone 329C, the one on the right is 15 per cent of Pantone 2617C.
Once I do this however, I can see irregular, vertical 'banding' on the gradient. I've tried printing this out and the banding is clearly evident on the proof.
I've tried exactly the same process in Illustrator CS3 and the result is exactly the same - clear banding visible both on screen and in print.
Am I doing something wrong?
Many thanks for any help.

Answer 1

Christoph is right. The best method is a combination of Add Noise and Steves method. The advantage with noise - its random and not a 2 pixel check pattern. The 2 pixel check pattern will only work with low res images.
These are the best methods to non-destructively apply the necessary noise to a gradient.
 1 - apply a pattern overlay layer style. First you generate a noise pattern (6 or 4% monochromatic noise applied to a neutral 128,128,128 grey ) and blur this noise by a tiny amount 1 or 2 pixels. Then make a seemless pattern from this about 200 pixels square. Then go to the pattern overlay layer style. Blend the pattern using Overlay or Soft Light at 70% opacity.
 2 - make a new layer. Fill with the pattern generated above or just fill the layer with gray and noise/blur it. Blend 70% using Soft Light or Overlay