Rust Stains on some of my clothes

Rust stains can occur after washing your clothes for several different reasons:

1. They can come from the rust developing in your washing machine itself
2. They can come from the water you are using to wash your clothes if the mineral content is high. This will be amplified if you use bleach, because bleach will set the stains.
3. Bacteria that chemically reacts with older iron pipes. While many newer homes contain PVC piping, city water is often supplied using iron pipes.
4. When house or city water lines have been disturbed by maintenance work, back flushing or vigorous movement, such as what occurs in an earthquake.
5. An area suffering from drought and low water reserves can cause sediment to accumulate within pipes. Rust spot coloring on clothes can range from brown or yellow to bright orange due to sediment diversity.

You can read more about this here.

Hope this helps!