Hi there I'm new to this forum. I have a 2004 v6 Mazda tribute. I have a high pitched whining noise which stops when I touch the brake pedal, it is also there when I stop the vehicle, and again until I touch the brake then it stops. I guess there are two options the brake servo, or the the brake vac line check valve. The servos are about $700 and the check valve I'm sure is way cheaper. I have done the brake pedal test where you turn the car off and put your foot on the brake pedal, the pedal is supposed to rise if there is a problem. It didn't. So can anyone help.