Hi HankMcSpank

It's hard to describe noise levels in words but I'll try.

I have a water cooled spindle and can report that when it arrived I ran up the motor resting on towel and it was barely audible. Just a faint whine that you would probably not hear in an adjacent room in the house. They use a different motor type, unlike the router with it's noisy universal motor.

When I clamped it to my machine (with aluminium plates, gantry etc.) the noise levels increased noticeably as the vibrations were now being amplified by the cnc machine. It's a bit like those old musical toys which are quiet in your hand but are much louder if you rest them on the table.

That's not to say it was noisy on the machine, probably similar to a cordless drill. You could easily hold a conversation next to the machine.

Now things get different when you actually start cutting. Depending upon the material this is probably where things get the loudest. Still not at router level but you just can't escape the noise created by the bit cutting the material. If you are in the loft with a party wall to your neighbours there's a chance they will hear the cutting noise. Your only defense is to build an acoustic enclosure around the machine. Make the enclosure walls fairly heavy, have good seals especially the doors, and add absorption to the inside.

Hope this helps.