I dropped off the MINI yesterday and picked up my car, and now the rattle is fixed!! The first thing I noticed was how heavy the steering is. I was so used to it that it wasn't a problem. but after driving the MINI it felt like the power steering was broken.
And the brakes. While pulling out of the parking area I kept hitting the brakes too hard (almost coming to a complete stop each time I did it). The MINI needed quite a bit of pedal pressure to bring it to a stop, but not the E90.
Nevertheless, a few km's down the road it felt normal again.