John,
Lots of people are experiencing the same thing and 99% of the time it turns out to be that your low in brake fluid in the reservoir. As your brakes wear out the fluid in the reservoir drops down to fill in the lines when your pads have to be closer to the rotors. Make sure you use the right kind of brake fluid when topping off.
Of course you might be the 1% that's having a different problem, but check that first.
