Acutally, the unit is never "off", the only thing the power button controls is it providing video output and live recording. So, it is always running, thinking about things, recording shows, getting updates, etc. Anyway, it never actually powers off, and as such, the fan never stops running. You could consider trying to quiet the fan either by installing a quieter fan or by slowing down the fan. If you search, you will find several articles about quieting the fan.