To the OP, I had a similar pattern noise issue this past summer with my 7D, which was severe vertical striping. See my post on it at DPReview, here (image included at link)...http://forums.dpreview.com/forums/read.asp?forum=1019&message=39424620
The body had been back to Canon Irvine numerous times for this issue (in addition to repeated AF issues), with only "electrical adjustments" being listed as work done on my service reports, and Canon service reporting that the body was within normal performance specifications. After this (intermittent) noise issue cropped up again in late September, I sent my 7D into the Irvine facility again with sample prints and a very sternly worded letter that the issue was not fixed, that I assumed a faulty sensor was at play, and that I demanded a complete repair or a full replacement body.
My repairs with Canon usually take less than 10 business days door to door. Interestingly, this trip was exactly 3 weeks door to door - the longest turn around I've ever had with Irvine. Maybe it was a seasonal issue, but I'm assuming more work was being done on my camera. This was confirmed when my camera arrived and I read the service report. It was EXTREMELY vague, but in a nutshell it said something along the lines of, "testing was done and it was determined that a faulty internal component was producing noise in images. The internal component was replaced."
This was the first time in my 7D's seven visits to Canon that an actual part was replaced. I'm assuming the sensor was swapped out, but I'll never really know. If your noise issues persist, I'd suggest sending the body into Irvine with image samples, and a firm letter demanding concrete results.
Best of luck.