Some owners of 2016-2022 Mazda CX-3, 2013-2022 CX-5 and 2017-2018 Mazda3 vehicles may complain about a tapping or knocking noise coming from the rear seat area after a fuel fill.
The concern will likely occur if the fuel tank is overfilled (more fuel is added after the fuel pump nozzle shuts off automatically) or filled up normally in high ambient temperatures and the fuel expands.
No repair is needed. Explain to the customer not to continue filling after the nozzle shuts off. Overfilling also presents a potential overflow and fire hazard.