Originally Posted by
SiZT
Roots are the loudest whilst on the throttle, twin-screws are loud'ish at idle, centrifugal's don't really make any noise.
P.S The noise is nothing to do with the gears
Clearly you've never heard many centrifugals then, including mine.
The gears create the majority of the noise. The belt drive can create some noise, but modern serpentine belts run pretty quiet. Even a cogged belt now can be pretty quiet.
They design belts to be as quiet as possible.
But gears, especially if straight cut, there is little way of quietening them down easily.