If it is singing when the brakes are not engaged, then that means you are getting contact between pads and rotor when you should not.

Try a couple of things:

-clean and lube the setup. A little friction can make the return spring hang up a bit and the pads end up dragging lightly on the rotors.
-add a little more spring tension to the system. I know my BB7's have a spring adjustment screw on them. If so, then just give it a turn. If not, then maybe you could pop the pads and spring out and flex the spring out a bit to give it more tension.

jim