If the device is rattling, it could mean that one of the parts is loose. A nut or screw could be unsecured to the tool, and the vibrations could cause the part to rattle. If this is not the case, the noise could also be attributed to friction. Lubrication of the spindle could suffice.
Also take a look [[DeWalt D28110 Troubleshooting|here]] for troubleshooting the angle grinder.