I would hope your plumber and expert could find the problem. I see 4 possibilities. 1=galvanized piping that has rusted on the inside. If you have any replace it by repiping. If you don't see any, look for galvanized nipples in the tub spout and around shower valve, water heater inlet and outlet, and maybe in the walls where the faucets come out. It don't take long for a nipple to develop rust inside.
2=water heater. 17 years is a very long time for the water heater. If you haven't replaced the anode rod in a while, then the water has rusted the inside of the tank and it is getting in the water. It won't be long till it rusts through and begins leaking all over the floor.
3=rusted steel well casing. The casing could be rusted and flaking off in the water.
4=the well water. Get it tested and the test should tell you if the rust is originating from the water or from a pipe source.
There may be others but that is the likely ones IMHO. Good luck and post back when you find out what it is. Start a new post if it takes more than a few days.