Are the air purifiers loud on high?

Almost every model we reviewed is quiet on its lowest/sleep setting (often 22–25 dB) and noticeably louder on the top speed. Specialist-community threads in particular flag noise on the highest fan setting as a common complaint, so if you plan to run a purifier in a bedroom, prioritize models with a strong sleep mode and a CADR high enough that you won't need to run it on max.