I am stumped by a noise coming from the rear of my Volvo (275000Km). The noise is metallic and is a loud grating noise like a brake puck with no lining scraping against a rotor. It happens at any speed but only intermittently and for a few seconds at a time. I pulled the brake rotors and inspected the e-brake hardware and replaced the two rear most u-joints, the rubber support and the centre bearing within the past 6 months. the rubber bushings on the trailing arms etc. seem OK. I am thinlking maybe a wheel bearing but the fact that it happens only occasionally makes me wonder. Any ideas would be graetfully appreciated.