If the _rotor_ is being eaten, then you're not hearing the 'brake pad worn out' sensor. Usually, that starts going first, then you change the brakes. If you don't change the brakes, then the metal of the brake pad starts directly contacting the rotor, which gives the huge rattle/grind/screaming - destroying the rotor.
The first thing I'd check is to see if there's adequate play for the pads in the caliper guide slots. I know my wife's old car required my using a grinder on the pads to get clean travel - the castings, on even the good pads, weren't cleaned up properly. The second is if you have the little chromed metal pad guides that sit in the caliper guides slots, and the third is to make sure that you used adequate lubricant in the guides. (Those chrome clips aren't absolutely necessary, but they sure make a difference if you're in an area vulnerable to corrosion, like by the ocean, or a northern state) The last is to make sure that the caliper slide pins and rubber boots are clean and lubricated.
Another, less likely culprit, is that the rotors are being warped by excessive heat, and just chew the pads up like mad. If so, then see the above anyway.
The only other thing I could think of is if you ride with one foot on the brake and the other on the gas; that kind of person, however, doesn't tend to do their own repairs and maintenance.