I've been thinking about this as well. I kind of want one of those ducted fume extractors, but don't want to pay the hundreds of dollars they cost, so I was looking into a shopvac and probably a speed controller to build off of. The Vacmaster brand units claim a relatively low noise figure--74dB, versus like 90+ for typical vacs or 66dB for the Fein vacuum. It might be interesting to experiment with a few noise remediation techniques, like a more substantial muffler fitted to the outlet, or adding some weight to the lid for damping, or baffling the motor cooling vents.