Small update: I was urged to bring the car back in for service after emailing my displeasure to a high ranking executive at BMWNA. The dealership is conferring with the regional engineer as to what to do next to stop the noises. I actually got a call to come pick the car up yesterday, but while I was on my way they called back and said they found another rattle during a test drive...
The whole situation is really unfortunate, but my hope is that they are either able to stop the noises once and for all, or get me into another 7-Series immediately.
Another question for the sub: Do any fellow 750i owners have their cars show up as Alpina B7s when the VIN is run? I've had this problem since day one and what really sucks is that my insurance agent is forced to charge me the B7 rates until BMW sends him a letter stating that the car is indeed a 750. I've reached out to several people at corporate and no one seems to know what's going on.