Weird noise pattern viewable in ACR but not CS5

I was at a wedding for my SIL over the weekend and took a few shots for her. I was reviewing the images in ACR and it appeared as though there was a weird noise pattern in all of the images from my 40D at ISO 400. It almost looked like vertical banding.

However, when I would zoom in a bit, the banding disappeared. Also - when I moved the images to CS5, the banding was also not present. At first I thought my images had looked like this all along and I had never noticed it before I got my new 24 inch monitor (previously had only a 13 inch laptop).

Obviously this isnt the case since it isnt visible when the images are converted, so I really dont have a problem - Im just curious.

Any thoughts?

What's your color space in the camera, ACR and CS5 ?

Do you have the latest updates ?

What's your bit depth and resolution output in ACR ?

I think Im using sRGB in all places, but those are good points - Ill have to check.

Yes, I do have the latest updates.

Resolution is the highest I can out of my 40D, Ill have to check the bit depth.

All good points, thanks for the tips - Ill look into them all.

Maybe if you posted a screen capture -- one that clearly shows the problem?