Originally Posted by spartanKid

I believe it was friction facts testing that showed that the quietest drivetrain is not necessarily the one with the lowest friction. For example, waxed chains are very fast, but tend to be a bit noisier than the quietest liquid lubed chains.

If I had to hazard a guess why, it would be that the heavier, thicker lubes dampen noise the best, but aren't necessarily the fastest or more efficient because of the viscosity.