ever hear the old adage, "if it ain't broke don't fix it" I think that should apply here. I believe the few incidents we see to be isolated and now (psychosematic (sp)) kicks in and everyone hears noises. My e46 rattled and never gave an issue. In fact these older bimmers were issue enough for BMW to release a statement reqarding normal vanos noises and what was normal and what was excessive. This is nothing new. In fact a good test is to rev the car up steady to like 3k and listen for a rattle by the front of the head. All these cars make noises, some more than others.
If anyone wants to test my theory, when the car is cold, pull the fuse for the fuel pump and crank the engine for 15 sec to build oil pressure and then replace fuse and start the car. See if you still hear the rattle.
IMO I would be pretty hesitant to let BMW rip apart the top end of the car due to some excessive noises espeically if the car drives fine and hasn't thrown any codes yet.