Pbutler1,
I thought maybe your fan was running off the batteries, fast and loud. It's not supposed to do that. In the old 5n1, that was not even possible. In Atlas, the solar panels appear to wire to the main board. Some have suggested that's because solar electricity helps run the main board, stretching battery life. A wiring glitch or defective component could let battery power flow the wrong way into the motor.
Keep an eye on your unit. If you burn through batteries like crazy, you may have to contact AcuRite.