This bulletin applies to 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 noise may be heard with vibration during partial to full engine load in higher gears. The cause may be tuning of the rear suspension mount for the differential.
To confirm the concern, note the following steps:
1. If a knocking noise is heard, drive the vehicle for five to 10 miles to warm up the driveline. Operate the engine in the range of 3000-5500 rom. Let off the throttle and then immediately step back on the accelerator. Perform these steps in Comfort, Sport and Sport Plus modes.
2. If a humming/droning/vibration is found, drive the vehicle with the transmission in sixth gear. Operate the engine in the range of 2500-3100 rpm or 4500-5500 rpm.
If the noise is confirmed, replace the rear differential suspension mount using polyurethane rubber rear mount P/N 33 17 094 690.
