The car uses the rear screen heater assembly as the aerial via filter units installed under the rear pillar panels. The panels are removed by simply sliding them forward, but first you must remove the rear seat base (a sharp pull upwards does the job as there are no screws etc to remove). Next remove the seat sections nearest to the doors by removing the bolt that secures the bottom of the seat section to the inner sill. The seat section then just pushes upwards and unhooks. The panel can then be slid out. On my car (a UK 1997 750i), there are two of these filters, one for AM and one for FM. Good luck.