We had that problem about a year ago. After replacing several expensive parts, the tech apparently determined that it was a buildup of ink on the carriage wheels/guides that was creating friction/chattering as it moved along the rod. He didn't seem to have seen that problem before, and it took the guy 3 days to get it fixed (by eventually replacing the entire carriage). Replacing the carriage solved the problem and we haven't had the problem since, but they charged us for all of the guy's time and the extra parts that he replaced before finding the actual problem. Great printer otherwise, but that service call was a debacle and it was alarming for them to A. Not recognize what the problem was right away. B. Charge us for the time and trial and error it took for them to figure out what the problem was and how to fix it.