Inspect BMW Rear Differential Mounts

This bulletin applies to 2017 BMW M3, M4 and M2 vehicles built up to July 31, 2018. A hard knocking noise may be heard from the rear axle area during load reversals; or a humming/droning noise may be heard with vibration during partial to full engine load in higher gears. The cause may be the tuning of the rear suspension mount for the differential. Replace the rear differential mount if the specified sound can be reproduced as detailed here:

1. Confirm that the noise is being produced by the tuning of the differential mount in one of the following testing conditions:
2. For a knocking noise, drive the vehicle for 5-10 miles to warm up the driveline. Operate the engine in the range of 3000-5500 rpm. Let off the throttle and then immediately step back onto the accelerator. Perform these steps in Comfort, Sport and Sport Plus modes.
3. For a vibration/droning noise, drive the vehicle with the transmission n sixth gear. Operate the engine in the range of 2500-3100 rpm (the noise may also be produced in the 4500-5500 rpm range).

If the noise was reproduced, replace the rear differential mounts using polyurethane rubber mounts P/N 33 17 8 094 690. Check wheel alignment following the repair.