I suspect that the noise may just be the sound of a spring attached to the pedal, to return the pedal: it probably makes this noise with the engine running you just don't hear it then.
As for the switch not operating when the ignition is off, the mechanical part (the part that it likely to make a click) DOES operate with the ignition off, but the electrical (silent) part does not. And suggesting it may be the pads coming into contact with the disk is flawed, the pads dont get retracted so as there is a gap, and you wouldnt be lilely to hear them even if they did.