2006 M5. My post experience is different from what BMW service people might say about noises, as well as most posts I have seen by people surmising about what the noises might be.
Mine made the diesel-style rattle at idle when hot. Didn't worry too much since so many people had this noise (Top Gear too).
Added a supercharger with a cast aluminum intake manifold. Two things soon became clear:
The stock plastic intake manifold is designed to make noise. I lost about 25-30% of the "exhaust" sound when adding the supercharger kit. Many other supercharger owners may not notice this as most seem to already run aftermarket exhausts that may overpower the intake noise.
The rattling sounds at idle are gone. Probably because the plastic intake plenum is no longer there, and that plastic manifold was obviously designed to be an engine noise amplifier.
Sorry, I would vote on your poll but my answer is not an option...

 

I am a little late on this one. I, as well have an '06, M5. I hear "noises" from the front of the engine as well. There are two highly respected independent BMW shops in my area. Both have said the engine sounds perfect. My car just hit 100K on the clock. I have done the SMG trans fluid flush, diff oil change, and coolant flush. Hope it survives another 100K

 

What are you talking about? I have neither of those sounds