Q: Car squealing when I add water to the radiator

The noise you are hearing is cold water hitting hot metal and turning to steam, like a steam whistle. You may have an intake or head gasket leaking where the head and intake meet in the front, or back, of the top of your motor. This is very common. I recommend that you have a mechanic, like the ones from YourMechanic, come by to verify the source of the squealing noise; a pressure test may be done to see if your engine has the leaks I described.