Ford trucks 2013-2018 with IWE actuator can experience an erratic grinding noise: The noise will usually occur on acceleration in 2WD mode; The hub itself could be defective or there can be a vacuum issue; The vacuum switch on the firewall should be tested for vacuum and signal; Use a vacuum pump to test hoses and both IWE actuators; Replace switch, hoses, or actuators accordingly; and ensure the latest TCCM calibration has been uploaded.