I just purchased a rebuilt rear brake caliper from the local Volvo dealer, the caliper was in a sealed box with all the appropriate Volvo factory part tags as well. Inspecting the caliper I noticed that both pistons have a step about 1 mm. deep ground into them across the face of the pistons. This step is approximately across 25% of the surface and the low part of both steps are facing towards the rotors direction of rotation. What gives? Is this some sort of modification to alleviate brake squeal? I have never seen this done on other vehicles brakes. Does anyone have some information on this? The original caliper did not have this "feature".