1979ak

Hi All, When I wash my clothes in my washing maching, there are sometimes some red marks (looks a bit like dried blood) but more likely to be rust I guess, left on some of the lighter clothing. These marks are not easy to remove - and I seem to be writing off a lot of light shirts and t-shirts. Has anyone seen this problem before, and if so what is the best way of curing it. Any help would be gratefully appreciated. Kind regards, Akkers