Originally Posted by
noimagination
I dislike using superlatives, therefore: all other things being equal, a quieter drivetrain is probably better than a noisier one, since the sound is generated by converting mechanical energy to sound. Efficiency losses due to noise are likely miniscule compared to other sources of mechanical inefficiency (IANAE - I am not an engineer), so I wouldn't worry about some drivetrain noise.
Once the bike is set up properly, the thing to notice is a change in drivetrain noise (type or volume), not necessarily the absolute volume. We've all run across the rider with the grinding/squeaking drivetrain, so just don't be that guy.
Sawdust in car gearboxes makes them quieter, but it's not very mechanically efficient. Using a thick oil based lube on a chain will have a similar effect, but again it's not very efficient. Straight cut gears are much noiser than helical gears, but they are more efficient. So mechanical noise and efficiency are not necessarily related. So I kind of agree with you here. I wouldn't worry about drivetrain noise and it doesn't imply that your silent 2012 drivetrain is more efficient. It's probably just heavier and a bit less resonant through the frame etc.