I've had the 40 and 10's. They are not dead silent. Tunzes are definately quieter, but that is a design compromise by having the motor external and not damped by water.
If you run them full bore all the time, they might be annoying. Some are louder than others for some reason. Maintenance is easy. I put the wetside in a vinegar bath for 30-60 min every so many months, then rinse and return to the tank. Takes a tiny bit of effort to re-align to minimize vibrations.