FJ Cruiser brake pedal noise

I just bought a certified used 2007 FJ Cruiser with over 36.000 miles on it, I didn't notice it at the time because I had the radio on, when I turned the radio off I hear a air noise when the engine is on and I press the brake pedal, I have isolated it to the brake pedal piston (if that is what it is called), whch is covered by a dust boot. I wonder is this sound normal for the FJ Cruiser or it should be looked a by Toyota service?