I just wanted to describe a 'problem' I've had and a solution I discovered. Interestingly, my problem and the solution are nearly identical to those of the Baders, described here:
I had a resonant moan/droan that began at about 1100 rpm and peaked in intensity (volume) at about 1500 rpm, and was gone by 1900rpm or so. It was almost louder than the engine, and could be felt as a slight vibration in the foot area at it's peak. Based on Erik's write up, I decided to take my exhaust apart to check things out. The one thing that's crucial to this is a universal joint for the socket set, since nearly everything is in a confined space. Besides this, a basic metric set plus wrenches will do.
I disassembled the pieces connecting the headers to the turbo, and then the post-turbo pipe (downpipe)...3 pipes in total. After looking around with a good flashlight and these pieces removed, I noticed a bolt just sitting under the turbo, on the engine block. It turns out that this bolt was one of three that connects the turbo the it's pedestal, the back one just as Erik describes was missing in his unit. Sadly, my turbo had been rebuilt by the dealer less than a year ago, and I'm sure their inattention lead to my situation. This whole process took only a couple hours.
I replaced this bolt, and tightened every other bolt I could reach (hardly any of them would budge), and put everything back together. A test drive results in my noise being very greatly reduced, but not totally gone. I may go back and re-torque some of the exhaust junctions, but probably not any time soon. It's good to know everything is back together like it should be, but disappointing to think that the dealer didn't/couldn't do it. I'm still under bumper to bumper warranty!