I think one of my many rattles is coming from the same area on my M3W on the same side, which is passenger on my LHD car. I will see if I can get a bit of old rubber floor mat between the body and the chassis. When I have the boot floor out later this year to fit the new ATR coil spring/shocks, I will also investigate the worst rattle from around where the roll hoop goes through the body.
Wilson