I also have a 2009 335i xDrive with the same problem with the radio cutting out. I've had the car for just over a year and have it in 7 times to try to find a fix for the issue. So far, they have tried downloading new software, replaced the radio, replaced some module and now want to replace the amp. LOVE the car but this is getting to be pretty painful. Has anyone else had the problem and had it repaired...if so, what was the repair?