Bruce,
I have listened for any whistling sounds and have heard none. Haven't tried driving the car with the vacuum line to the booster disconnected. I will try this if the rain ever quits. Is the check valve you refer to in the unit itself and can I get to it? I can put a vacuum plug over the plug that comes out of the intake to block the vacuum. I know then the brakes will be hard to use as I had a power unit go completely out on one of my other cars once. And since this has been this way since 1996 or 97 and has never gotten worse that is what has me really confused as if that takes much. Power brakess are not one of my strong points.
Thanks,
Ron
