Noise is subjective. What's quiet to others might not be for you. Location of the tank will also dictate how much noise is tolerable. If the tank is near where you sleep or study, even the slightest nose can bother you. It also depends if it's a constant noise(I actually like this for sleeping) or erratic noise.
With that said, I would not categorize the MP40QD I've used quiet by any mean when you have it pulse mode. Tolerable? Yes. But not silent.
I've used both MP and Tunze. For noise(or lack of), I would go with Tunze. I'm currently using Two 6255s and they're much quieter than the two MP60QD I've tried and also can push the sand around at the other end of the 6' peninsular. MP60QD was not able to do that.
However, I've been successfull using MP40QD on a smaller tank but I have one at each end of the tank.