This is much worse than a loose bolt, I'm afraid. This is just another N54 engine issue that is just now surfacing at 48k miles. Thankfully I have extended warranty on this, but I really just don't think that BMW owners should have these kinds of problems.
The most frustrating thing to me is that I will now have to take the car in 5 or 6 times, which is a complete waste of my time, before BMW will actually do anything to fix it. Software, adjustments, etc. are just BS ways of skirting the real issue. The turbos need to be replaced probably, even though the car 'drives' fine.