Every once in awhile we'll find an article of clothes with ugly (and
seemingly unremovable) spots after removing it from our washer. It was a
mere annoyance when it would happen to a t-shirt but now a nice skirt of
my wife's has been ruined!

We have rust in our well water that does this once in a while. A water
treatment guy (for what this is worth -- I don't know how true or false it
is) said there is two kinds of iron problems you can have -- one is when the
iron is oxidized, and comes out of the tap orange. the other is when the
iron is dissolved in solution, and doesn't turn orange until it hits the
oxygen in the air. He said we have both kinds. The first I was able to
filter out with a whole house filter, the second, we still have some issues
with.

The other possibility is that something rustable got in the wash from a
pocket -- a nail, a screw, something else from the shop like a small drill
bit...I've done it. My wife hates that.