Fans stopping and starting on Dell Powerconnect

Hi guys,

So i have 2 stacks of Dell Powerconnect, two 5224 and two 6224. On stack 1 (5224) One of the units has the fans changing speed level from 1 to 0 and after like 5-20 min they go again from 0 to 1.

There are some times that this goes for more than 1 hour, back and forth,

The temperature is always at 41 and the server room is never hot so i don't really know why this happens.

Also curious why only one unit on this stack. Does anyone know why this happens?

Thanks!