2005 Chevrolet Suburban, I have a weird knocking noise that sounds like it is coming from fairly close in to the instrument panel, in the engine compartment. The noise starts when the vehicle key is turned, and regardless of the engine being on or not. The noise isnt very consistent either. I also noticed vibration in the brake pedal, but was thinking that was just a bad rotor, could both problems be a faulty break booster?