Only when the hot water is on does the hot water heater whistle. I called bosch technical support and was told tha LP pressure from the LP tank was either too hih or too low. They suggested I call the gas compan7y and have put a Manometer on the LP line. Today I had the gas co. service rep come out, checked pressure with meter, all in spec. Not sure what to do now as the whistling noise can be heard amile away.