This bulletin applies to 2018 Audi Q5 and 2017-2018 A4, S4, A5, S5 and Q7 models. After pulling away, a slight rattling or clicking noise may be heard from the front of the vehicle at about 25 mph. It might be also felt slightly through the accelerator and brake pedal.
The ABS/ESP system performs a short self-check during which all valves of the hydraulic unit are operated at the same time and the return pump runs briefly. This functionality ensures the pre-load of the ABS pump and the readiness of the Pre-Sense System if required.
The self-check is necessary for correct operation of the ABS/ESP system. The resulting noises are unavoidable.
This will help explain the issue to a customer who may be concerned.