It's hard to imagine exactly what you mean. One tiny flaw in the "tile" will repeat itself over and over. Is the background all one uniform colour? If it's a scan it won't be.
Is there a border or line you don't notice until you tile the image?
Does it go from light to dark, meaning when it's tiled there's a sudden change in colour?
Have you tried cutting the image in half and putting the halves back to back like I did in this tile I made for the carry-on films?(IMG:http://img176.imageshack.us/img176/7363/carryontilevk6.th.jpg
Perhaps you could post an example of your pattern.