A bushing has worn out to the point the armature is now coming in contact with the yoke (magnet barrel). You can probably see wear on the armature, and maybe even run your finger inside the magnet barrel and feel that it is not perfectly smooth (or perfectly round) any more.
I'm not sure if this has ever been documented happening on an XT starter, but most surprising to me that it is on a starter that only has 12,000 miles.

I don't have a lot of confidence in an aftermarket starter for $40. But keep us posted on how it works out. This would be a great starter alternative if it does work out.

2004 XT225 purchased new in October 2004 0 miles. Current miles over 27,000.