Hi can anyone help. I have an Audi 2016 a4 sline. I have been getting a knocking noise which I think is coming from the rear of the car. This only happens at low. Speed when I’m driving in urban areas. It’s fine at high speed. It’s gradually getting worse. It sounds like something is rattling under my car. I’ve had in in my local garage they can’t find the problem. Any ideas will be much appreciated. Steve