This problem seems to affect a lot of C-70's. I have found the anti rattle spring on the caliper hitting the rotor. When the brakes are applyied, the pads push the spring away from the rotor and the noise stops. Volvo has issued a different design spring to corect the problem. Simply remove the pad retaining pins and original spring, and replace the spring. To verify if this is your noise, remove the wheel and spin the rotor, then reposition the spring with a screwdriver and see if it stops scraping. Also, you may see evidence on the edge of the rotor of contact.