I have the same issue. The squeak can only be heard with the ac and radio off. The shop foreman actually pointed it out on a test drive for another issue. There is a green plastic bushing that dries out and requires the removal of the entire dash. These are the foreman's word so I take it at face value. I still have not had the time to have it fixed.

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2011 550xi Carbon Black/Oyster, M-Sport, Premium Package, Technology Package, Electronic Damper Control, Dynamic Drive, Comfort Access, Active Seats, Surround Cameras

2013 X5 5.0 Space Grey/Black, M-Sport, Premium Package, Technology Package, Comfort Access, Surround Cameras