Inside your washer tub, do you see any marks that were scrached and rusting?
Do you have a piece of metal or something like that logdged in the tub around the agitator that could be the culprit?
Have you removed the agitator and looked around and inspected the situation?
Have you ran a non load cycle with bleach or baking soda or TSP or something like that to clean out the system?
Last resort, the actual pump on the bottom of the unit is like a counch shell, or like an ear drum. could you have something lodged in there that is rusting and depositing the rust on the clothes on the in water cycle?
On an inspection of your water lines all in the house and especially to the washer, do you see any rust deposits in the lines?