I have a high-pitched shrill sound when the 2nd floor shower is turned on. I shut down valves, let air out, but it didn't work. The noise is coming from the pressure regulator area in the basement (the regulator is only 3 years old!). A plumber suggested it's either the toilet or regulator, but he wouldn't elaborate. The noise also happens when the clothes washer is used-also in the basement. Can anyone help me?