Still sounds like the cv boot to me. The "brake sensor" is just a small piece of metal that touches the edge of the rotor when the pad is worn down to a certain point. It makes a grinding/screeching sound, it isnt pleasant, but unless your brake pad is loose, (which I'm sure its not or you would have other problems) there is no reason for it to click.

that many miles could mean you need brakes soon, you can always check to see if the "brake sensor" is touching when you take the tire off.