The fan runs continuously and at the same speed, when connected to a computer. I would not call it "noisy" but it is clearly audible, and might be disturbing for sensitive persons in a very quiet environment. I got used to it, even if I would have preferred a silent unit. It is difficult to place it far from the computer due to the short length of the TB3 cable provided with it. Note: my MacBook Pro M1 Max remains completely silent and the bay itself contains only SSD, therefore the fan is the only source of noise in my configuration.. Out of topic but may be interesting: it is connected to the Mac over a OWC TB4 Dock and I am absolutely satisfied with the performance.