It's those pads.
I even have a particular comment about them in my book, on page IIIB-9. They almost killed me during a Denver rainstorm.
Find some pads that have, at the VERY least, sintered bronze bits in the pucks. You can likely look at yours right now and find an opaque, dark, smooth, solid, granite-like surface on them that will last many thousands of miles, because IT DOESN'T WEAR OFF TO STOP THE BIKE.
Better yet: dig around and find some asbestos ones. The fibers that will fall off those pucks will only hurt the lungs of the bureaucrats who work for places like EPA or DOT, which might even help the rest of us out...
...end of rant...