1998 Chevy Z-71 Brake Problem

I have a 98 Chevrolet Z-71 Pick up. Lately, the brakes have been making a sound not unlike a Bronx cheer, with accompaning vibration through the pedal and followed by about an inch of slack pedal travel. Rotors, pads, and master cylinder are already ruled out (less than 1 year old). Any ideas.

Rotors, pads and master cylinder have been ruled out??? You know there are not really that many components in a brake system, and you have “ruled out” the ones that cause brake pedal travel problems, noise and vibrations. I would reconsider what you have ruled out. What does a “Bronx cheer” sound like anyway?

A passible Bronx cheer can be replicated by placing your mouth into the crook of your elbow and blowing. I’m thinking that it might have something to do with the vacuum assist.