Brought mine back today, they gave me a loaner X3 which does not exhibit the noise. I took the tech out and he heard the noise as well... so now it's back there. If you put some tape on the indentation, does the noise go away?
The tech I had on the ride along this morning said they had an ultra-sonic device there which they could use to diagnose these issues. He explained that even compressed air could jet up through cracked lift pads into the cabin, then out again. In other words, noises like this might have very complex jet-stream behavior which is hard to diagnose... Anyway, he seemed to imply that this device was capable of determining leaks in the cabin.
The service manager already thinks I'm a lunatic because most of their older guys can't hear the problem at all. I'm not sure what I'm going to do if they give it back to me without the problem fixed. If I wanted a noisy minivan I would have bought one...