I've noticed that with specific fans in my PC, like a Be Quiet fan, I start to fall asleep listening to it. I can try to resist falling asleep, but eventually it happens. Maybe it's due to the white noise, or the pitch, or something. But an Arctic one for example not at all. Why is this the case? Is it because maybe one has thinner blades, is louder, or less loud? What is the factor causing this? I bought a 120mm "Silent" fan from eBay that runs on USB, and while you can definitely hear it and it's pretty noisy, I still fall asleep. Maybe it's because they are silent fans? Maybe silent fans are made different compared to normal ones?