Mineral deposits in the plumbing. If you have hard water then your wash machine, dish washer and other water using appliances most likely have mineral build up not only in the supply lines, but in their pumps and internal lines as well. There are products one can use to remove the minerals in machines. http://www.diylife.com/2007/07/24/make-your-washing-machine-more-efficient/ and http://www.essortment.com/home/cleanwashingma_sokn.htm Frankly, I set up my machine with cold water, I fill it completely with water (highest load setting) and pour in half a gallon of white vinegar. I keep the lid open which allows it to agitate and pump water through its system but does not allow it to drain/spin. If yours will drain/spin then watch it closely. When its finished with its first agitation turn off the machine, there will be vinegar water in its plumbing. Let is sit about an hour. Reset the machine to the start of the cycle, close the lid and let it run completely through. Rinse it by resetting the complete cycle, again on the highest load setting and let it run completely through without any stopping. We can not use bleach with our white here at home. Our well has a bit of iron and sulfur in the water content which reacts with the bleach to leave spots and even causes discoloration. We use Mrs. Stewart's bluing to whiten whites. Also, check the lint trap and the hoses. The supply hoses have screens which may have 'sand' inside of them or rust chips or other stuff. If its rust chips the water flowing in/over the rust bits can lead to minor discoloration. Also check your laundry soap. If you are using powder, add it first to the machine, turn on the machine, get water in their and swirl the water with the soap to dissolve the soap, Then add the cloths when the machine is half full for the load.