Digital BW, The Print

I have some strange "noise" for lack of a better word in this  
step-wedge: 
 
http://hiddenworld.net:81/wild-wedge.jpg 
 
Can anyone tell me what might be causing this?   
 
This was printed with Quad-Tone Rip, using Linux, and printed 
landscape mode.

"Ranyart" 
> I have some strange "noise" for lack of a better word in this  
> step-wedge: 
>  
> http://hiddenworld.net:81/wild-wedge.jpg 

Could it be the printer rollers?