The percussion motor on both Pure-Wave CM5 and CM7 were tested in a lab to be under 40 decibels. This is equivalent to a library and quieter than most massagers of this caliber if not all.
Keep in mind Pure-Wave is a machine for treating muscle pain and providing massage therapy. While it is quiet it's nearly impossible for us to make it silent given the power that it delivers and the price people are willing to pay for such a device.
You can actually kind of gauge the loudness by watching these 2 videos we made.