I had a similar squeaking issue with my drivers front seat within a few 100 miles of getting the car. I complained when I brought it in for something else. They put a "felt strip" between the seat and the mounting area. It still squeaked about 25 miles later, but then I made a very minor seating position adjustment, leaned it back just a hair and the squeak has been gone for almost 3000 miles at this point.
I agree with everyone that it was extremely annoying.

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Adam
2012 X5 35i Sport, Sparkling Bronze Metallic
2011 MBZ GL450
Past rides
2009 MBZ GL450
2009 MBZ E-350 Sport
2006 MBZ CLS500
1980 Porsche 911 Targa, Petrol Blue