I have the same noise and brought it up to my dealer. There are two causes that they offered. The first possible cause is a need for lubrication at the base of the steering column where it meets the firewall (which they performed). The second is a piece of plastic which was described as a ring around the airbag which comes loose or binds to make that plasticky noise. They will perform that fix as soon as I schedule an appointment. I don't always here it, though. Sometimes it's very faint, others it's quite noticeable. I don't like it either, but it's a problem of which they've been aware for a while.

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2005 X5 4.8is/ Imola Red/ Cream
2002 ///M Roadster/ Alpine White/ Imola Red (SOLD!)
2008 ///M5 ordered and on it's way!!