The crossflow fan in your Grobo will consistently run and produce a very low hum, similar to a white noise machine. 

The crossflow fan is in the top of your unit, it is responsible for pulling the air from your grow chamber through your carbon filter and out through the back grate of your unit. 

It is not completely silent, therefore, if you need to put it in a room with frequent traffic, you may notice the sound more often due to your proximity to the Grobo. 

The intake fans [Gen1] and the moveable fans [Gen2] will turn on based on your recipe stage. When do my fans turn on?

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