My newest fan assembly is really quiet. I have to be within 3 feet to hear it. My older one I could hear fro 15 feet or so. Get your head right next to it, and then cover the Solar panel with your hand, you should be able to hear a change. How much hotter are you running, and how are you determining this?
I've been as close as a few inches and I don't hear it. Does it require full direct sunlight? It was early morning when I last checked, maybe not enough sun? Can I trick it with a flash light? Its pretty cloudy now. I may possibly have malfunctioning fans.
Looks like I'm running 6-8 degrees warmer than a shaded thermometer and surrounding PWSs.