Do you have any plug in accessories? In my e53, I couldn't tune the radio when I had my USB plug in to charge my phone. The DC> DC power adapters are notoriously bad for creating radio interference or audible hum.

Make an audio recording or scan witg FFT program to figure out what is the frequency.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)