BMW X1 E84 MY14 AM radio not working

[Greg1]

Radio in my parents BMW X1 sDrive 18d E84 MY14 has developed a lot of noise on the AM band making it basically unlistenable due to all the interference etc. FM, CD and other audio all work perfectly. Just AM radio that has the problem.

Had local BMW service centre take a look at the system when it was last in for service but they were unable to find/fix the problem. Without physically swapping the head unit for another one which they did not have at the time and for them to continue fixing they wanted to charge a huge hourly fee to continue diagnosing the problem.

Was wondering if anyone here has any ideas on the likely cause of the AM radio problem and has any suggestions to fix?

The audio system is the stock factory iDrive setup with screen and the following controls