I have had mine running for a week now. I played with all the settings to see how it would work. It does have a small click when it starts. From what I understand, this is what prevents the prop from starting backwards. With them on a lower interval, like 30 seconds or 1 min, I could notice it more because it was more frequently switching. I ran it at 6 hours for a day and for now I've settled on 15 min intervals. That way it only clicks a few times an hour and I can't even notice it. I occasionally hear it flip over, but that's only if the house is empty and quiet. So far I'm happy with them. Of course, since only 1 is running at a time, I want a little more flow from each of them. I may eventually upgrade to the next step, which I believe is the magnum 5. We'll see, I'm happy for now.