This very real and repeatable optical illusion is referred to as "moiré" pattern. They occur on models that use small repeatable patterns. It is a combination of the resolution of the rendered image, the resolution of the monitor, or the resolution of the printer that can intensify this affect.
Render software like AccURender can not completely eliminate this effect but users can work to lessen its appearance. Here are some suggestions:
Antialiasing is a process where more than one ray is shot per pixel in an attempt to better resolve the value of the pixel. Five levels of antialiasing are available. Increasing the antialiasing level adds considerable rendering time. Highest triggers more than 16 samples per pixel for every pixel in your rendering.
It is by far the slowest, but provides the best quality. When this option is selected antialiasing is improved and moiré patterns are reduced or almost eliminated. This is done In the Raytrace Settings dialog box, on the Quality tab. Use the antialiasing with caution - render times change drastically.
Also known as jitter, noise adds some randomness to each ray's pixel position. A small amount of noise is helpful in removing such raytracing artifacts as moiré patterns. Heavily patterned renderings may require more noise. This setting varies between 0.0 and 0.25 representing a fraction of a pixel. Try a noise setting of .5. Increasing the noise too much will make the rendering look fuzzy or out of focus.
Increase the resolution of the final rendering. In the Raytrace Settings dialog box, on the Main tab, use the controls to customize the raytrace settings. If you are rendering to the AutoCAD viewport, your choices are limited to whole number multiples of the viewport resolution. If you are rendering to the WalkAbout window, more standard choices display. Enter values in the X and Y boxes to set a custom resolution. Depending on your screen resolution, you many not notice the improvement until you send out a print.
While the antialiasing and increasing the final rendering resolution is really nice, it is really slow. Note that the patterns you see on screen may or may not show up in print - depending on your resolution. Try a test print to the output device. It may just be a result of the display resolution. Don't be overly concerned with the pattern which may disappeared when sent to a high-resolution printer. What you are looking at is essentially an interference pattern with your monitor's resolution.
When scanning pre-printed images or photos, use a program like PhotoShop to add noise and even despeckle once (maybe twice). It softens the image but eliminates the moiré pattern. You may also use this same PhotoShop technique for post processing the final rendered image.
Instead of using a brick size of 2x8, use 6x24 instead. It will decrease the moire effect and at a distance will not be noticeable anyway.