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Have a 2009 535xit since new, just hit 10k last week. A few weeks ago I noticed a sound like air leaking from a compressor happening intermittently when stepping on the brakes. The sound appears to eminate from the right rear seat area. Brought it to the dealer to have them test it and of course it didn't occur while mechanic was in car. He said there was a common problem with caliper squeaks but this is a definite escaping air under pressure sound. If any one has suggestions or experience with this please let me know. Thanks for your help, from Seattle.