warped rotors would be the cause, the max runout is .004". when replacing rotors on a BMW x5, the pads are to be replaced as well, I would only recommending using OEM rotors. Here is my reasoning. The X5 rotors are warp friendly, say you replace them from some online vender or aftermarket company, most do not come with warranty. If you install the OEM rotor from BMW, now your covered for the next 2 years with parts warranty including labor. If bmw is paying to replace the part, they are going to pay the Labor. I have a customer who always brings his car to us every 1.5 years with brake shimmy at highway speeds. Every 1.5 years he gets new front rotors and pads free of charge. Because he purchased the parts from BMW. We torque the caliper bracket at 110NM and the Wheels to 140NM. and they always seem to warp no matter what. So go with OEM.