I'm guessing this is some sort of vacuum problem... but I haven't been able to nail down the source or solution.

When I'm at a stop, with the car running, I can press down further on my brake pedal and hear this whining / squealing / high pitched noise. The noise gets progressively louder and then fainter as I press the pedal down towards the floor. There is no noise when I let off the brake pedal - and rolling down the road.

This noise seems to come and go. Sometimes it's gone all together. That's what makes it so hard to diagnose. Can't isolate it to hot / cold weather or engine temp.

This IS NOT a brake rotor / brake caliper issue.
This noise happens at a FULL STOP.

Any suggestions??
My sincere thanks in advance - this forum is awesome!!

 

Maybe something to do with your ABS system?

 

the way the vacuum booster works is that it has a diaphragm inside that helps move the piston to compress the fluid when you push the brakes, therefore moving brake fluid etc etc. If this has a small tear in it, it would cause that noise I THINK you're describing.