I am comparing my 2008 M5 with my friend's 2006. There are 2 major mechanical differences that have me thinking.
1st, my motor makes a more throaty burbly noise when revved and it's definitely louder than his. When revved his goes voooooooooooooom, mine goes voom burble vooom burble vooom.
When I let off the gas on mine it feels like the motor is twisting (this is in N in the driveway), his doesn't.

Of course, when cruising on the highway the cars are indistinguishable except for the additional rumble of my motor. Any ideas why that may be?

2nd difference is the SMG downshifting to 2nd. Mine clanks (not all the time) when slowing down to a light/stop sign and going to 2nd. His is completely silent.

So, the final question is, do these cars differ that much in sound and behaviour or should I be asking the dealer to check things out?