The noisy fan really varies by device. My Air Graident Basic DIY makes very little noise. I have another device I got earlier, a "Lonicera" (some chinese brand) and it looks like it has an extremely similar Plantower PM sensor inside, which is what has the little fan ... but it is often way noiser and rattle-y, the fan is clearly somewhat malfunctioning. I've taken it mostly apart, but it didn't seem worth the effort to go the last mile to fix or replace it.