I saw a LOT o black flakes in the bathwater today and now recall that there've been similar flakes in the bathwater during the fall--which I attributed to my picking up dirt etc. in my hair in doing yard work with a leaf blower.
I've checked the screens on the faucets on the 1st floor and no flakes. So I'm assuming that they're not coming from a common source such as the water heater.
We had the upstairs bathroom plumbing redone 15 years ago with new copper piping, Moen faucets etc. There've been no plumbing problems before.
I see no apparent leaks or other indication of faulty neoprene seals etc.