O.K. guys and gals, here, I believe, is a new one...

If you find out that the filter is NOT the problem, you might look for a piece of steel pipe in the lines somewhere. Being a plumber I found over the years that some home owners would use steel nipples to fix their plumbing. Look around faucets or water heater for steel. Water that sits in steel over night will turn black for a second and then clear up. That is why they used galvanized pipe years ago, it's all plastic now.